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sysv: don't call sb_bread() with pointers_lock held 

syzbot is reporting sleep in atomic context in SysV filesystem [1], for
sb_bread() is called with rw_spinlock held.

A "write_lock(&pointers_lock) => read_lock(&pointers_lock) deadlock" bug
and a "sb_bread() with write_lock(&pointers_lock)" bug were introduced by
"Replace BKL for chain locking with sysvfs-private rwlock" in Linux 2.5.12.

Then, "[PATCH] err1-40: sysvfs locking fix" in Linux 2.6.8 fixed the
former bug by moving pointers_lock lock to the callers, but instead
introduced a "sb_bread() with read_lock(&pointers_lock)" bug (which made
this problem easier to hit).

Al Viro suggested that why not to do like get_branch()/get_block()/
find_shared() in Minix filesystem does. And doing like that is almost a
revert of "[PATCH] err1-40: sysvfs locking fix" except that get_branch()
 from with find_shared() is called without write_lock(&pointers_lock).

Reported-by: syzbot <syzbot+69b40dc5fd40f32c199f@syzkaller.appspotmail.com>
Link: https://syzkaller.appspot.com/bug?extid=69b40dc5fd40f32c199f
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Link: https://lore.kernel.org/r/0d195f93-a22a-49a2-0020-103534d6f7f6@I-love.SAKURA.ne.jp
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Tetsuo Handa 2023-04-10 21:04:50 +09:00 committed by Christian Brauner
parent 85f273a6a1
commit f123dc8638
1 changed files with 4 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
fs/sysv/itree.c
View File

@ -83,9 +83,6 @@ static inline sysv_zone_t *block_end(struct buffer_head *bh)
return (sysv_zone_t*)((char*)bh->b_data + bh->b_size);
}
/*
* Requires read_lock(&pointers_lock) or write_lock(&pointers_lock)
*/
static Indirect *get_branch(struct inode *inode,
int depth,
int offsets[],
@ -105,15 +102,18 @@ static Indirect *get_branch(struct inode *inode,
bh = sb_bread(sb, block);
if (!bh)
goto failure;
read_lock(&pointers_lock);
if (!verify_chain(chain, p))
goto changed;
add_chain(++p, bh, (sysv_zone_t*)bh->b_data + *++offsets);
read_unlock(&pointers_lock);
if (!p->key)
goto no_block;
}
return NULL;
changed:
read_unlock(&pointers_lock);
brelse(bh);
*err = -EAGAIN;
goto no_block;
@ -219,9 +219,7 @@ static int get_block(struct inode *inode, sector_t iblock, struct buffer_head *b
goto out;
reread:
read_lock(&pointers_lock);
partial = get_branch(inode, depth, offsets, chain, &err);
read_unlock(&pointers_lock);
/* Simplest case - block found, no allocation needed */
if (!partial) {
@ -291,9 +289,9 @@ static Indirect *find_shared(struct inode *inode,
*top = 0;
for (k = depth; k > 1 && !offsets[k-1]; k--)
;
partial = get_branch(inode, k, offsets, chain, &err);
write_lock(&pointers_lock);
partial = get_branch(inode, k, offsets, chain, &err);
if (!partial)
partial = chain + k-1;
/*