In an effort to separate intentional arithmetic wrap-around from unexpected wrap-around, we need to refactor places that depend on this kind of math. One of the most common code patterns of this is: VAR + value < VAR Notably, this is considered "undefined behavior" for signed and pointer types, which the kernel works around by using the -fno-strict-overflow option in the build[1] (which used to just be -fwrapv). Regardless, we want to get the kernel source to the position where we can meaningfully instrument arithmetic wrap-around conditions and catch them when they are unexpected, regardless of whether they are signed[2], unsigned[3], or pointer[4] types. Refactor open-coded pointer wrap-around addition test to use check_add_overflow(), retaining the result for later usage (which removes the redundant open-coded addition). This paves the way to enabling the wrap-around sanitizer in the future. Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1] Link: https://github.com/KSPP/linux/issues/26 [2] Link: https://github.com/KSPP/linux/issues/27 [3] Link: https://github.com/KSPP/linux/issues/344 [4] Cc: Steve French <sfrench@xxxxxxxxx> Cc: Paulo Alcantara <pc@xxxxxxxxxxxxx> Cc: Ronnie Sahlberg <lsahlber@xxxxxxxxxx> Cc: Shyam Prasad N <sprasad@xxxxxxxxxxxxx> Cc: Tom Talpey <tom@xxxxxxxxxx> Cc: linux-cifs@xxxxxxxxxxxxxxx Cc: samba-technical@xxxxxxxxxxxxxxx Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- fs/smb/client/readdir.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/fs/smb/client/readdir.c b/fs/smb/client/readdir.c index 94255401b38d..7715297359ab 100644 --- a/fs/smb/client/readdir.c +++ b/fs/smb/client/readdir.c @@ -467,12 +467,13 @@ static char *nxt_dir_entry(char *old_entry, char *end_of_smb, int level) pfData->FileNameLength; } else { u32 next_offset = le32_to_cpu(pDirInfo->NextEntryOffset); + char *sum; - if (old_entry + next_offset < old_entry) { + if (check_add_overflow(old_entry, next_offset, &sum)) { cifs_dbg(VFS, "Invalid offset %u\n", next_offset); return NULL; } - new_entry = old_entry + next_offset; + new_entry = sum; } cifs_dbg(FYI, "new entry %p old entry %p\n", new_entry, old_entry); /* validate that new_entry is not past end of SMB */ -- 2.34.1
