From: Eric Biggers <[email protected]>
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: 2c2eb7a300cd ("f2fs: Support case-insensitive file name lookups")
Cc: <[email protected]> # v5.4+
Cc: Al Viro <[email protected]>
Cc: Daniel Rosenberg <[email protected]>
Cc: Gabriel Krisman Bertazi <[email protected]>
Signed-off-by: Eric Biggers <[email protected]>
---
fs/f2fs/dir.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
index 44bfc464df787..5c179b72eb8a8 100644
--- a/fs/f2fs/dir.c
+++ b/fs/f2fs/dir.c
@@ -1083,6 +1083,7 @@ static int f2fs_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)) {
if (len != name->len)
@@ -1090,6 +1091,22 @@ static int f2fs_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) {
+ unsigned int i;
+
+ for (i = 0; i < len; i++)
+ strbuf[i] = READ_ONCE(str[i]);
+ strbuf[len] = 0;
+ qstr.name = strbuf;
+ }
+
return f2fs_ci_compare(inode, name, &qstr, false);
}
--
2.26.2
On 05/29, Eric Biggers wrote:
> From: Eric Biggers <[email protected]>
>
> 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: 2c2eb7a300cd ("f2fs: Support case-insensitive file name lookups")
> Cc: <[email protected]> # v5.4+
> Cc: Al Viro <[email protected]>
> Cc: Daniel Rosenberg <[email protected]>
> Cc: Gabriel Krisman Bertazi <[email protected]>
> Signed-off-by: Eric Biggers <[email protected]>
Acked-by: Jaegeuk Kim <[email protected]>
> ---
> fs/f2fs/dir.c | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
>
> diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
> index 44bfc464df787..5c179b72eb8a8 100644
> --- a/fs/f2fs/dir.c
> +++ b/fs/f2fs/dir.c
> @@ -1083,6 +1083,7 @@ static int f2fs_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)) {
> if (len != name->len)
> @@ -1090,6 +1091,22 @@ static int f2fs_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) {
> + unsigned int i;
> +
> + for (i = 0; i < len; i++)
> + strbuf[i] = READ_ONCE(str[i]);
> + strbuf[len] = 0;
> + qstr.name = strbuf;
> + }
> +
> return f2fs_ci_compare(inode, name, &qstr, false);
> }
>
> --
> 2.26.2