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![Jann Horn](/assets/img/avatar_default.png)
romfs has a superblock field that limits the size of the filesystem; data
beyond that limit is never accessed.
romfs_dev_read() fetches a caller-supplied number of bytes from the
backing device. It returns 0 on success or an error code on failure;
therefore, its API can't represent short reads, it's all-or-nothing.
However, when romfs_dev_read() detects that the requested operation would
cross the filesystem size limit, it currently silently truncates the
requested number of bytes. This e.g. means that when the content of a
file with size 0x1000 starts one byte before the filesystem size limit,
->readpage() will only fill a single byte of the supplied page while
leaving the rest uninitialized, leaking that uninitialized memory to
userspace.
Fix it by returning an error code instead of truncating the read when the
requested read operation would go beyond the end of the filesystem.
Fixes: da4458bda2
("NOMMU: Make it possible for RomFS to use MTD devices directly")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: David Howells <dhowells@redhat.com>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/20200818013202.2246365-1-jannh@google.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
287 lines
6.1 KiB
C
287 lines
6.1 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/* RomFS storage access routines
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*
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* Copyright © 2007 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*/
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#include <linux/fs.h>
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#include <linux/mtd/super.h>
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#include <linux/buffer_head.h>
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#include "internal.h"
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#if !defined(CONFIG_ROMFS_ON_MTD) && !defined(CONFIG_ROMFS_ON_BLOCK)
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#error no ROMFS backing store interface configured
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#endif
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#ifdef CONFIG_ROMFS_ON_MTD
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#define ROMFS_MTD_READ(sb, ...) mtd_read((sb)->s_mtd, ##__VA_ARGS__)
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/*
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* read data from an romfs image on an MTD device
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*/
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static int romfs_mtd_read(struct super_block *sb, unsigned long pos,
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void *buf, size_t buflen)
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{
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size_t rlen;
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int ret;
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ret = ROMFS_MTD_READ(sb, pos, buflen, &rlen, buf);
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return (ret < 0 || rlen != buflen) ? -EIO : 0;
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}
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/*
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* determine the length of a string in a romfs image on an MTD device
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*/
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static ssize_t romfs_mtd_strnlen(struct super_block *sb,
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unsigned long pos, size_t maxlen)
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{
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ssize_t n = 0;
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size_t segment;
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u_char buf[16], *p;
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size_t len;
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int ret;
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/* scan the string up to 16 bytes at a time */
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while (maxlen > 0) {
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segment = min_t(size_t, maxlen, 16);
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ret = ROMFS_MTD_READ(sb, pos, segment, &len, buf);
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if (ret < 0)
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return ret;
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p = memchr(buf, 0, len);
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if (p)
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return n + (p - buf);
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maxlen -= len;
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pos += len;
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n += len;
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}
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return n;
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}
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/*
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* compare a string to one in a romfs image on MTD
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* - return 1 if matched, 0 if differ, -ve if error
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*/
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static int romfs_mtd_strcmp(struct super_block *sb, unsigned long pos,
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const char *str, size_t size)
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{
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u_char buf[17];
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size_t len, segment;
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int ret;
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/* scan the string up to 16 bytes at a time, and attempt to grab the
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* trailing NUL whilst we're at it */
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buf[0] = 0xff;
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while (size > 0) {
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segment = min_t(size_t, size + 1, 17);
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ret = ROMFS_MTD_READ(sb, pos, segment, &len, buf);
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if (ret < 0)
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return ret;
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len--;
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if (memcmp(buf, str, len) != 0)
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return 0;
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buf[0] = buf[len];
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size -= len;
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pos += len;
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str += len;
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}
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/* check the trailing NUL was */
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if (buf[0])
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return 0;
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return 1;
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}
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#endif /* CONFIG_ROMFS_ON_MTD */
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#ifdef CONFIG_ROMFS_ON_BLOCK
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/*
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* read data from an romfs image on a block device
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*/
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static int romfs_blk_read(struct super_block *sb, unsigned long pos,
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void *buf, size_t buflen)
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{
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struct buffer_head *bh;
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unsigned long offset;
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size_t segment;
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/* copy the string up to blocksize bytes at a time */
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while (buflen > 0) {
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offset = pos & (ROMBSIZE - 1);
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segment = min_t(size_t, buflen, ROMBSIZE - offset);
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bh = sb_bread(sb, pos >> ROMBSBITS);
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if (!bh)
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return -EIO;
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memcpy(buf, bh->b_data + offset, segment);
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brelse(bh);
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buf += segment;
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buflen -= segment;
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pos += segment;
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}
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return 0;
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}
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/*
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* determine the length of a string in romfs on a block device
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*/
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static ssize_t romfs_blk_strnlen(struct super_block *sb,
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unsigned long pos, size_t limit)
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{
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struct buffer_head *bh;
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unsigned long offset;
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ssize_t n = 0;
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size_t segment;
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u_char *buf, *p;
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/* scan the string up to blocksize bytes at a time */
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while (limit > 0) {
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offset = pos & (ROMBSIZE - 1);
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segment = min_t(size_t, limit, ROMBSIZE - offset);
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bh = sb_bread(sb, pos >> ROMBSBITS);
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if (!bh)
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return -EIO;
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buf = bh->b_data + offset;
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p = memchr(buf, 0, segment);
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brelse(bh);
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if (p)
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return n + (p - buf);
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limit -= segment;
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pos += segment;
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n += segment;
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}
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return n;
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}
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/*
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* compare a string to one in a romfs image on a block device
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* - return 1 if matched, 0 if differ, -ve if error
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*/
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static int romfs_blk_strcmp(struct super_block *sb, unsigned long pos,
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const char *str, size_t size)
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{
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struct buffer_head *bh;
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unsigned long offset;
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size_t segment;
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bool matched, terminated = false;
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/* compare string up to a block at a time */
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while (size > 0) {
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offset = pos & (ROMBSIZE - 1);
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segment = min_t(size_t, size, ROMBSIZE - offset);
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bh = sb_bread(sb, pos >> ROMBSBITS);
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if (!bh)
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return -EIO;
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matched = (memcmp(bh->b_data + offset, str, segment) == 0);
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size -= segment;
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pos += segment;
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str += segment;
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if (matched && size == 0 && offset + segment < ROMBSIZE) {
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if (!bh->b_data[offset + segment])
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terminated = true;
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else
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matched = false;
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}
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brelse(bh);
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if (!matched)
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return 0;
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}
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if (!terminated) {
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/* the terminating NUL must be on the first byte of the next
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* block */
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BUG_ON((pos & (ROMBSIZE - 1)) != 0);
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bh = sb_bread(sb, pos >> ROMBSBITS);
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if (!bh)
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return -EIO;
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matched = !bh->b_data[0];
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brelse(bh);
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if (!matched)
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return 0;
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}
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return 1;
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}
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#endif /* CONFIG_ROMFS_ON_BLOCK */
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/*
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* read data from the romfs image
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*/
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int romfs_dev_read(struct super_block *sb, unsigned long pos,
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void *buf, size_t buflen)
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{
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size_t limit;
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limit = romfs_maxsize(sb);
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if (pos >= limit || buflen > limit - pos)
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return -EIO;
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#ifdef CONFIG_ROMFS_ON_MTD
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if (sb->s_mtd)
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return romfs_mtd_read(sb, pos, buf, buflen);
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#endif
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#ifdef CONFIG_ROMFS_ON_BLOCK
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if (sb->s_bdev)
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return romfs_blk_read(sb, pos, buf, buflen);
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#endif
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return -EIO;
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}
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/*
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* determine the length of a string in romfs
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*/
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ssize_t romfs_dev_strnlen(struct super_block *sb,
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unsigned long pos, size_t maxlen)
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{
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size_t limit;
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limit = romfs_maxsize(sb);
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if (pos >= limit)
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return -EIO;
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if (maxlen > limit - pos)
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maxlen = limit - pos;
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#ifdef CONFIG_ROMFS_ON_MTD
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if (sb->s_mtd)
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return romfs_mtd_strnlen(sb, pos, maxlen);
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#endif
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#ifdef CONFIG_ROMFS_ON_BLOCK
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if (sb->s_bdev)
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return romfs_blk_strnlen(sb, pos, maxlen);
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#endif
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return -EIO;
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}
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/*
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* compare a string to one in romfs
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* - the string to be compared to, str, may not be NUL-terminated; instead the
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* string is of the specified size
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* - return 1 if matched, 0 if differ, -ve if error
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*/
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int romfs_dev_strcmp(struct super_block *sb, unsigned long pos,
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const char *str, size_t size)
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{
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size_t limit;
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limit = romfs_maxsize(sb);
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if (pos >= limit)
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return -EIO;
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if (size > ROMFS_MAXFN)
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return -ENAMETOOLONG;
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if (size + 1 > limit - pos)
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return -EIO;
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#ifdef CONFIG_ROMFS_ON_MTD
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if (sb->s_mtd)
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return romfs_mtd_strcmp(sb, pos, str, size);
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#endif
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#ifdef CONFIG_ROMFS_ON_BLOCK
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if (sb->s_bdev)
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return romfs_blk_strcmp(sb, pos, str, size);
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#endif
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return -EIO;
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}
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