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authorEric Biggers <ebiggers@google.com>2020-06-01 13:08:05 -0700
committerJaegeuk Kim <jaegeuk@kernel.org>2020-06-08 20:37:53 -0700
commitfc3bb095ab02b9e7d89a069ade2cead15c64c504 (patch)
treedf6dd9f4f8b6594b8342f111a28a97070953f03d /fs/f2fs/dir.c
parent0b6d4ca04a86b9dababbb76e58d33c437e127b77 (diff)
f2fs: avoid utf8_strncasecmp() with unstable name
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: <stable@vger.kernel.org> # v5.4+ 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> Reviewed-by: Chao Yu <yuchao0@huawei.com> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Diffstat (limited to 'fs/f2fs/dir.c')
-rw-r--r--fs/f2fs/dir.c16
1 files changed, 16 insertions, 0 deletions
diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
index 29f70f2295cc..d35976785e8c 100644
--- a/fs/f2fs/dir.c
+++ b/fs/f2fs/dir.c
@@ -1114,11 +1114,27 @@ static int f2fs_d_compare(const struct dentry *dentry, unsigned int len,
const struct inode *dir = READ_ONCE(parent->d_inode);
const struct f2fs_sb_info *sbi = F2FS_SB(dentry->d_sb);
struct qstr entry = QSTR_INIT(str, len);
+ char strbuf[DNAME_INLINE_LEN];
int res;
if (!dir || !IS_CASEFOLDED(dir))
goto fallback;
+ /*
+ * 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;
+ entry.name = strbuf;
+ /* prevent compiler from optimizing out the temporary buffer */
+ barrier();
+ }
+
res = utf8_strncasecmp(sbi->s_encoding, name, &entry);
if (res >= 0)
return res;