Message ID | 20200601200805.59655-1-ebiggers@kernel.org |
---|---|
State | Not Applicable |
Headers | show |
Series | [v2] f2fs: avoid utf8_strncasecmp() with unstable name | expand |
On 2020/6/2 4:08, 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: 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> Thanks,
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;