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 --- 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); }