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R. Silva" , Bill Wendling , Justin Stitt , linux-kernel@vger.kernel.org Subject: [PATCH 14/82] smb: client: Refactor intentional wrap-around calculation Date: Mon, 22 Jan 2024 16:26:49 -0800 Message-Id: <20240123002814.1396804-14-keescook@chromium.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240122235208.work.748-kees@kernel.org> References: <20240122235208.work.748-kees@kernel.org> Precedence: bulk X-Mailing-List: linux-cifs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=2356; i=keescook@chromium.org; h=from:subject; bh=pqahPWCtiilVxi2Cwewikz7N45reJkQJ7UJUXEGvxo0=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBlrwgF+RrezY1R+vJeoB3MoQno65kcsaFJYE8T7 TFT3XWlULSJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCZa8IBQAKCRCJcvTf3G3A JghND/9sxXRpGBChydX6oXKHlWt5zCT0j1qCewzIX5EZfL6bLAAMMvbrryh0Kxi9Sj4hqZGsIHg LtEJVktXPEirje72RefP1RpOxo01UzeUOLmDOWUHMoB4B0z+XubPvEaAaQ93LFS0A5Cf2GSblOc Hx+I37mBMNSY3YGAsN9F86amVO0lc8gZY8oppvXg0goQD2o031eriElKHB3uK26o2m9SokcDyZW Q4di9IdRGvGZ4IPTbQ0R5Uc/QqdPqSBZ/tJyncI0bhVLAYKfqLdKCWvKzpFkbsxSnLFey7WJTtL N6JxOZoVgb+cu14E6OubQIRM4a2MF6lWjK/TSXxKa741TuGCCZWHVWy8HfQg/nEehtsBojQR5Ke n4ZK0eZDc+TVrnTYX09u87bgIwCCnlVBad9RNxR6MYfbB5PCTvmdApJodAX+eamo/22YvttIlV2 lHj7KOeoKn1Ybl67n+iX3eJgQ4EssmZnEZG7XmODkiw6AR1iDdWqIvIfoThRxBNs46UjYdzaIa/ KZn9l3Z/958uJ9DYefApgztvC4i06O+FIGSIYVn45yV+CgRlLA9VZjRlrzzgLoEgZrklYDey13J IlbCxjn/tjXnvRrqNAWm/i7hglaOoYH5il7sEsia1iH8bIkOkbWmiSISrRcH/ojibVnpKp/vaxx ikviov4jRF0L/Hg== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 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 Cc: Paulo Alcantara Cc: Ronnie Sahlberg Cc: Shyam Prasad N Cc: Tom Talpey Cc: linux-cifs@vger.kernel.org Cc: samba-technical@lists.samba.org Signed-off-by: Kees Cook --- 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 */