* [PATCH v2] ext4: avoid utf8_strncasecmp() with unstable name
@ 2020-06-01 20:05 Eric Biggers
2020-06-01 20:49 ` Andreas Dilger
2020-06-09 20:28 ` Eric Biggers
0 siblings, 2 replies; 4+ messages in thread
From: Eric Biggers @ 2020-06-01 20:05 UTC (permalink / raw)
To: linux-ext4
Cc: Daniel Rosenberg, stable, linux-f2fs-devel, Al Viro,
linux-fsdevel, Gabriel Krisman Bertazi
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>
---
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
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH v2] ext4: avoid utf8_strncasecmp() with unstable name
2020-06-01 20:05 [PATCH v2] ext4: avoid utf8_strncasecmp() with unstable name Eric Biggers
@ 2020-06-01 20:49 ` Andreas Dilger
2020-06-11 15:01 ` Theodore Y. Ts'o
2020-06-09 20:28 ` Eric Biggers
1 sibling, 1 reply; 4+ messages in thread
From: Andreas Dilger @ 2020-06-01 20:49 UTC (permalink / raw)
To: Eric Biggers
Cc: linux-ext4, Daniel Rosenberg, stable, linux-f2fs-devel, Al Viro,
linux-fsdevel, Gabriel Krisman Bertazi
[-- 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 --]
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] ext4: avoid utf8_strncasecmp() with unstable name
2020-06-01 20:49 ` Andreas Dilger
@ 2020-06-11 15:01 ` Theodore Y. Ts'o
0 siblings, 0 replies; 4+ messages in thread
From: Theodore Y. Ts'o @ 2020-06-11 15:01 UTC (permalink / raw)
To: Andreas Dilger
Cc: Eric Biggers, linux-ext4, Daniel Rosenberg, stable,
linux-f2fs-devel, Al Viro, linux-fsdevel,
Gabriel Krisman Bertazi
On Mon, Jun 01, 2020 at 02:49:51PM -0600, Andreas Dilger wrote:
> 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>
Thanks, applied.
- Ted
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] ext4: avoid utf8_strncasecmp() with unstable name
2020-06-01 20:05 [PATCH v2] ext4: avoid utf8_strncasecmp() with unstable name Eric Biggers
2020-06-01 20:49 ` Andreas Dilger
@ 2020-06-09 20:28 ` Eric Biggers
1 sibling, 0 replies; 4+ messages in thread
From: Eric Biggers @ 2020-06-09 20:28 UTC (permalink / raw)
To: Theodore Ts'o
Cc: Daniel Rosenberg, stable, linux-ext4, linux-f2fs-devel, Al Viro,
linux-fsdevel, Gabriel Krisman Bertazi
On Mon, Jun 01, 2020 at 01:05:43PM -0700, Eric Biggers 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>
> ---
>
> v2: use memcpy() + barrier() instead of a byte-by-byte copy.
>
> fs/ext4/dir.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
Ted, could you take this through the ext4 tree as a fix for 5.8?
The f2fs patch has been merged already.
- Eric
^ permalink raw reply [flat|nested] 4+ messages in thread
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2020-06-01 20:49 ` Andreas Dilger
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2020-06-09 20:28 ` Eric Biggers
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