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From: "Theodore Y. Ts'o" <tytso@mit.edu>
To: Eric Biggers <ebiggers@kernel.org>
Cc: linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-f2fs-devel@lists.sourceforge.net,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Daniel Rosenberg <drosen@google.com>,
	Gabriel Krisman Bertazi <krisman@collabora.com>
Subject: Re: [PATCH] ext4: fix race conditions in ->d_compare() and ->d_hash()
Date: Fri, 24 Jan 2020 22:35:22 -0500	[thread overview]
Message-ID: <20200125033522.GM147870@mit.edu> (raw)
In-Reply-To: <20200124041234.159740-1-ebiggers@kernel.org>

On Thu, Jan 23, 2020 at 08:12:34PM -0800, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.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@zeniv.linux.org.uk>
> Fixes: b886ee3e778e ("ext4: Support case-insensitive file name lookups")
> Cc: <stable@vger.kernel.org> # v5.2+
> Signed-off-by: Eric Biggers <ebiggers@google.com>

Thanks, applied.

						- Ted

      parent reply	other threads:[~2020-01-25  3:35 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-24  4:12 [PATCH] ext4: fix race conditions in ->d_compare() and ->d_hash() Eric Biggers
2020-01-24  5:04 ` Gao Xiang
2020-01-24  5:16   ` Eric Biggers
2020-01-24  5:27     ` Gao Xiang
2020-01-24  5:53       ` Eric Biggers
2020-01-24  5:34     ` Gao Xiang
2020-01-24  5:42       ` Eric Biggers
2020-01-24  6:15         ` Gao Xiang
2020-01-24 18:12           ` Eric Biggers
2020-01-24 18:31             ` Al Viro
2020-01-25  3:35 ` Theodore Y. Ts'o [this message]

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