On 05/29, Eric Biggers wrote: > From: Eric Biggers <ebiggers@xxxxxxxxxx> > > 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@xxxxxxxxxxxxxxx> # v5.4+ > Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > Cc: Daniel Rosenberg <drosen@xxxxxxxxxx> > Cc: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxxxx> > Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> Acked-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx> > --- > 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