From: Andreas Dilger <adilger@dilger.ca>
To: Eric Biggers <ebiggers@kernel.org>
Cc: linux-ext4@vger.kernel.org, Daniel Rosenberg <drosen@google.com>,
stable@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net,
Al Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel@vger.kernel.org,
Gabriel Krisman Bertazi <krisman@collabora.co.uk>
Subject: Re: [PATCH v2] ext4: avoid utf8_strncasecmp() with unstable name
Date: Mon, 1 Jun 2020 14:49:51 -0600 [thread overview]
Message-ID: <E876FECB-300E-471B-A790-D44F2F1A3F9A@dilger.ca> (raw)
In-Reply-To: <20200601200543.59417-1-ebiggers@kernel.org>
[-- Attachment #1: Type: text/plain, Size: 2523 bytes --]
On Jun 1, 2020, at 2:05 PM, Eric Biggers <ebiggers@kernel.org> wrote:
>
> From: Eric Biggers <ebiggers@google.com>
>
> If the dentry name passed to ->d_compare() fits in dentry::d_iname, then
> it may be concurrently modified by a rename. This can cause undefined
> behavior (possibly out-of-bounds memory accesses or crashes) in
> utf8_strncasecmp(), since fs/unicode/ isn't written to handle strings
> that may be concurrently modified.
>
> Fix this by first copying the filename to a stack buffer if needed.
> This way we get a stable snapshot of the filename.
>
> Fixes: b886ee3e778e ("ext4: Support case-insensitive file name lookups")
> Cc: <stable@vger.kernel.org> # v5.2+
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: Daniel Rosenberg <drosen@google.com>
> Cc: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
> Signed-off-by: Eric Biggers <ebiggers@google.com>
LGTM.
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
> ---
>
> v2: use memcpy() + barrier() instead of a byte-by-byte copy.
>
> fs/ext4/dir.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
> index c654205f648dd..1d82336b1cd45 100644
> --- a/fs/ext4/dir.c
> +++ b/fs/ext4/dir.c
> @@ -675,6 +675,7 @@ static int ext4_d_compare(const struct dentry *dentry, unsigned int len,
> struct qstr qstr = {.name = str, .len = len };
> const struct dentry *parent = READ_ONCE(dentry->d_parent);
> const struct inode *inode = READ_ONCE(parent->d_inode);
> + char strbuf[DNAME_INLINE_LEN];
>
> if (!inode || !IS_CASEFOLDED(inode) ||
> !EXT4_SB(inode->i_sb)->s_encoding) {
> @@ -683,6 +684,21 @@ static int ext4_d_compare(const struct dentry *dentry, unsigned int len,
> return memcmp(str, name->name, len);
> }
>
> + /*
> + * If the dentry name is stored in-line, then it may be concurrently
> + * modified by a rename. If this happens, the VFS will eventually retry
> + * the lookup, so it doesn't matter what ->d_compare() returns.
> + * However, it's unsafe to call utf8_strncasecmp() with an unstable
> + * string. Therefore, we have to copy the name into a temporary buffer.
> + */
> + if (len <= DNAME_INLINE_LEN - 1) {
> + memcpy(strbuf, str, len);
> + strbuf[len] = 0;
> + qstr.name = strbuf;
> + /* prevent compiler from optimizing out the temporary buffer */
> + barrier();
> + }
> +
> return ext4_ci_compare(inode, name, &qstr, false);
> }
>
> --
> 2.26.2
>
Cheers, Andreas
[-- Attachment #2: Message signed with OpenPGP --]
[-- Type: application/pgp-signature, Size: 873 bytes --]
next prev parent reply other threads:[~2020-06-01 20:49 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-01 20:05 [PATCH v2] ext4: avoid utf8_strncasecmp() with unstable name Eric Biggers
2020-06-01 20:49 ` Andreas Dilger [this message]
2020-06-11 15:01 ` Theodore Y. Ts'o
2020-06-09 20:28 ` Eric Biggers
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=E876FECB-300E-471B-A790-D44F2F1A3F9A@dilger.ca \
--to=adilger@dilger.ca \
--cc=drosen@google.com \
--cc=ebiggers@kernel.org \
--cc=krisman@collabora.co.uk \
--cc=linux-ext4@vger.kernel.org \
--cc=linux-f2fs-devel@lists.sourceforge.net \
--cc=linux-fsdevel@vger.kernel.org \
--cc=stable@vger.kernel.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).