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Date: Fri, 24 Jan 2020 22:35:22 -0500 From: "Theodore Y. Ts'o" <tytso@....edu> To: Eric Biggers <ebiggers@...nel.org> Cc: linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net, Alexander Viro <viro@...iv.linux.org.uk>, Daniel Rosenberg <drosen@...gle.com>, Gabriel Krisman Bertazi <krisman@...labora.com> Subject: Re: [PATCH] ext4: fix race conditions in ->d_compare() and ->d_hash() On Thu, Jan 23, 2020 at 08:12:34PM -0800, Eric Biggers wrote: > From: Eric Biggers <ebiggers@...gle.com> > > Since ->d_compare() and ->d_hash() can be called in RCU-walk mode, > ->d_parent and ->d_inode can be concurrently modified, and in > particular, ->d_inode may be changed to NULL. For ext4_d_hash() this > resulted in a reproducible NULL dereference if a lookup is done in a > directory being deleted, e.g. with: > > int main() > { > if (fork()) { > for (;;) { > mkdir("subdir", 0700); > rmdir("subdir"); > } > } else { > for (;;) > access("subdir/file", 0); > } > } > > ... or by running the 't_encrypted_d_revalidate' program from xfstests. > Both repros work in any directory on a filesystem with the encoding > feature, even if the directory doesn't actually have the casefold flag. > > I couldn't reproduce a crash in ext4_d_compare(), but it appears that a > similar crash is possible there. > > Fix these bugs by reading ->d_parent and ->d_inode using READ_ONCE() and > falling back to the case sensitive behavior if the inode is NULL. > > Reported-by: Al Viro <viro@...iv.linux.org.uk> > Fixes: b886ee3e778e ("ext4: Support case-insensitive file name lookups") > Cc: <stable@...r.kernel.org> # v5.2+ > Signed-off-by: Eric Biggers <ebiggers@...gle.com> Thanks, applied. - Ted
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