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: 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 ---
v2: Use memcpy() + barrier() instead of a byte-by-byte copy. Also rebased onto f2fs/dev.
fs/f2fs/dir.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+)
diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c index 29f70f2295cce..d35976785e8c5 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;