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ext4: fix unaligned memory access in ext4_fc_reserve_space()

Browse source 
As is done elsewhere in the file, build the struct ext4_fc_tl on the
stack and memcpy() it into the buffer, rather than directly writing it
to a potentially-unaligned location in the buffer.

Fixes: aa75f4d3da ("ext4: main fast-commit commit path")
Cc: <stable@vger.kernel.org> # v5.10+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20221106224841.279231-6-ebiggers@kernel.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Eric Biggers 2022-11-06 14:48:39 -08:00 committed by Theodore Ts'o
parent 64b4a25c3d
commit 8415ce07ec
1 changed files with 21 additions and 18 deletions
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39
fs/ext4/fast_commit.c
View file

@ -675,6 +675,15 @@ static void ext4_fc_submit_bh(struct super_block *sb, bool is_tail)
/* Ext4 commit path routines */
/* memcpy to fc reserved space and update CRC */
static void *ext4_fc_memcpy(struct super_block *sb, void *dst, const void *src,
int len, u32 *crc)
{
if (crc)
*crc = ext4_chksum(EXT4_SB(sb), *crc, src, len);
return memcpy(dst, src, len);
}
/* memzero and update CRC */
static void *ext4_fc_memzero(struct super_block *sb, void *dst, int len,
u32 *crc)
@ -700,12 +709,13 @@ static void *ext4_fc_memzero(struct super_block *sb, void *dst, int len,
*/
static u8 *ext4_fc_reserve_space(struct super_block *sb, int len, u32 *crc)
{
struct ext4_fc_tl *tl;
struct ext4_fc_tl tl;
struct ext4_sb_info *sbi = EXT4_SB(sb);
struct buffer_head *bh;
int bsize = sbi->s_journal->j_blocksize;
int ret, off = sbi->s_fc_bytes % bsize;
int pad_len;
u8 *dst;
/*
* After allocating len, we should have space at least for a 0 byte
@ -729,16 +739,18 @@ static u8 *ext4_fc_reserve_space(struct super_block *sb, int len, u32 *crc)
return sbi->s_fc_bh->b_data + off;
}
/* Need to add PAD tag */
tl = (struct ext4_fc_tl *)(sbi->s_fc_bh->b_data + off);
tl->fc_tag = cpu_to_le16(EXT4_FC_TAG_PAD);
dst = sbi->s_fc_bh->b_data + off;
tl.fc_tag = cpu_to_le16(EXT4_FC_TAG_PAD);
pad_len = bsize - off - 1 - EXT4_FC_TAG_BASE_LEN;
tl->fc_len = cpu_to_le16(pad_len);
if (crc)
*crc = ext4_chksum(sbi, *crc, tl, EXT4_FC_TAG_BASE_LEN);
if (pad_len > 0)
ext4_fc_memzero(sb, tl + 1, pad_len, crc);
tl.fc_len = cpu_to_le16(pad_len);
ext4_fc_memcpy(sb, dst, &tl, EXT4_FC_TAG_BASE_LEN, crc);
dst += EXT4_FC_TAG_BASE_LEN;
if (pad_len > 0) {
ext4_fc_memzero(sb, dst, pad_len, crc);
dst += pad_len;
}
/* Don't leak uninitialized memory in the unused last byte. */
*((u8 *)(tl + 1) + pad_len) = 0;
*dst = 0;
ext4_fc_submit_bh(sb, false);
@ -750,15 +762,6 @@ static u8 *ext4_fc_reserve_space(struct super_block *sb, int len, u32 *crc)
return sbi->s_fc_bh->b_data;
}
/* memcpy to fc reserved space and update CRC */
static void *ext4_fc_memcpy(struct super_block *sb, void *dst, const void *src,
int len, u32 *crc)
{
if (crc)
*crc = ext4_chksum(EXT4_SB(sb), *crc, src, len);
return memcpy(dst, src, len);
}
/*
* Complete a fast commit by writing tail tag.
*