| Message ID | 20200530060418.221707-1-ebiggers@kernel.org |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | f2fs: avoid utf8_strncasecmp() with unstable name | expand |
On 05/29, 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> Acked-by: Jaegeuk Kim <jaegeuk@kernel.org> > --- > 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
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); }