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 wrap-around addition test to use add_would_overflow(). This paves the way to enabling the wrap-around sanitizers 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/smb2pdu.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/smb/client/smb2pdu.c b/fs/smb/client/smb2pdu.c index 288199f0b987..85399525f0a7 100644 --- a/fs/smb/client/smb2pdu.c +++ b/fs/smb/client/smb2pdu.c @@ -5007,7 +5007,7 @@ num_entries(int infotype, char *bufstart, char *end_of_buf, char **lastentry, entryptr = bufstart; while (1) { - if (entryptr + next_offset < entryptr || + if (add_would_overflow(entryptr, next_offset) || entryptr + next_offset > end_of_buf || entryptr + next_offset + size > end_of_buf) { cifs_dbg(VFS, "malformed search entry would overflow\n"); @@ -5023,7 +5023,7 @@ num_entries(int infotype, char *bufstart, char *end_of_buf, char **lastentry, len = le32_to_cpu(dir_info->FileNameLength); if (len < 0 || - entryptr + len < entryptr || + add_would_overflow(entryptr, len) || entryptr + len > end_of_buf || entryptr + len + size > end_of_buf) { cifs_dbg(VFS, "directory entry name would overflow frame end of buf %p\n", -- 2.34.1
