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authorTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>2023-04-10 21:04:50 +0900
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2024-04-13 12:50:15 +0200
commit13b33feb2ebddc2b1aa607f553566b18a4af1d76 (patch)
tree97f2ccc818ee4e53b74497cdf33e3f3d4248356c
parent004402ec227732308871a6127f0b967cf2a293cd (diff)
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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: 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> Signed-off-by: Sasha Levin <sashal@kernel.org>
-rw-r--r--fs/sysv/itree.c10
1 files changed, 4 insertions, 6 deletions
diff --git a/fs/sysv/itree.c b/fs/sysv/itree.c
index e3d1673b8ec9..ef9bcfeec21a 100644
--- a/fs/sysv/itree.c
+++ b/fs/sysv/itree.c
@@ -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;
/*