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Commit 1b4fe801 authored by Tetsuo Handa's avatar Tetsuo Handa Committed by Greg Kroah-Hartman
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sysv: don't call sb_bread() with pointers_lock held 



[ Upstream commit f123dc86388cb669c3d6322702dc441abc35c31e ]

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: default avatarsyzbot <syzbot+69b40dc5fd40f32c199f@syzkaller.appspotmail.com>
Link: https://syzkaller.appspot.com/bug?extid=69b40dc5fd40f32c199f


Suggested-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarTetsuo 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: default avatarChristian Brauner <brauner@kernel.org>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent e04cae53

fs/sysv/itree.c

+4 −6
Original line number Diff line number Diff line
@@ -82,9 +82,6 @@ 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[],
@@ -104,15 +101,18 @@ 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;
@@ -218,9 +218,7 @@ 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) {
@@ -290,9 +288,9 @@ 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;

	/*