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author | 2019-03-28 17:38:29 +0200 | |
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committer | 2019-05-08 13:25:53 +0200 | |
commit | acf3062a7e1ccf67c6f7e7c28671a6708fde63b0 (patch) | |
tree | f4dda7c6c24f36eac36b9cb56f5e35f8bdfbfbf6 /fs/overlayfs/dir.c | |
parent | ovl: check the capability before cred overridden (diff) | |
download | linux-acf3062a7e1ccf67c6f7e7c28671a6708fde63b0.tar.gz linux-acf3062a7e1ccf67c6f7e7c28671a6708fde63b0.tar.bz2 linux-acf3062a7e1ccf67c6f7e7c28671a6708fde63b0.zip |
ovl: relax WARN_ON() for overlapping layers use case
This nasty little syzbot repro:
https://syzkaller.appspot.com/x/repro.syz?x=12c7a94f400000
Creates overlay mounts where the same directory is both in upper and lower
layers. Simplified example:
mkdir foo work
mount -t overlay none foo -o"lowerdir=.,upperdir=foo,workdir=work"
The repro runs several threads in parallel that attempt to chdir into foo
and attempt to symlink/rename/exec/mkdir the file bar.
The repro hits a WARN_ON() I placed in ovl_instantiate(), which suggests
that an overlay inode already exists in cache and is hashed by the pointer
of the real upper dentry that ovl_create_real() has just created. At the
point of the WARN_ON(), for overlay dir inode lock is held and upper dir
inode lock, so at first, I did not see how this was possible.
On a closer look, I see that after ovl_create_real(), because of the
overlapping upper and lower layers, a lookup by another thread can find the
file foo/bar that was just created in upper layer, at overlay path
foo/foo/bar and hash the an overlay inode with the new real dentry as lower
dentry. This is possible because the overlay directory foo/foo is not
locked and the upper dentry foo/bar is in dcache, so ovl_lookup() can find
it without taking upper dir inode shared lock.
Overlapping layers is considered a wrong setup which would result in
unexpected behavior, but it shouldn't crash the kernel and it shouldn't
trigger WARN_ON() either, so relax this WARN_ON() and leave a pr_warn()
instead to cover all cases of failure to get an overlay inode.
The error returned from failure to insert new inode to cache with
inode_insert5() was changed to -EEXIST, to distinguish from the error
-ENOMEM returned on failure to get/allocate inode with iget5_locked().
Reported-by: syzbot+9c69c282adc4edd2b540@syzkaller.appspotmail.com
Fixes: 01b39dcc9568 ("ovl: use inode_insert5() to hash a newly...")
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Diffstat (limited to 'fs/overlayfs/dir.c')
-rw-r--r-- | fs/overlayfs/dir.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c index 82c129bfe58d..93872bb50230 100644 --- a/fs/overlayfs/dir.c +++ b/fs/overlayfs/dir.c @@ -260,7 +260,7 @@ static int ovl_instantiate(struct dentry *dentry, struct inode *inode, * hashed directory inode aliases. */ inode = ovl_get_inode(dentry->d_sb, &oip); - if (WARN_ON(IS_ERR(inode))) + if (IS_ERR(inode)) return PTR_ERR(inode); } else { WARN_ON(ovl_inode_real(inode) != d_inode(newdentry)); |