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R. Silva" , Bill Wendling , Justin Stitt , linux-kernel@vger.kernel.org Subject: [PATCH 19/82] fs: Refactor intentional wrap-around calculation Date: Mon, 22 Jan 2024 16:26:54 -0800 Message-Id: <20240123002814.1396804-19-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-hardening@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=2642; i=keescook@chromium.org; h=from:subject; bh=hmcJNNt4Q4VRdZF2vWAi73bsrPppPr3nSkhgxxWjJIU=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBlrwgFKlHII6LhFKix+ewETmVbpfBbbfsybJbPD x+7qNyR682JAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCZa8IBQAKCRCJcvTf3G3A JliJD/sHf6ZqD8B/KWziPKmgyfqtW/R2omfg5NRF8ncdgxikerGRRFZGCvxzR4FW8MnjOxVf1uq VTlOujj9IdXmUGBNs6tlOuMkwDYDNxnpu2AhJz2L1ONpzLxW1Wo9TMy8M28suhDxJcE4bIhyVGL Fx2SEqEqstNDAG3Rd3j69TdEahfsyFepNOoEczntilqiJVXn+EVQfiYKnLqJOs/ClIXcT4I3UA0 K5aspcqb7nZa9d9oLHl/gnMr+7tzhUthPyt2nmE9yXR1trn1C7UxLbzym+BovDdAEmBNHATqitV gowcGG8q+UqAhrey3vsLtf5HImIOfkVd+TOcmaqoeKn0pdU+2ClklkZWWuSPZ487SM0cmDnz2C1 iGtEgxQSBrtf6GBC2d/etauF2TPzcSWLiA50TwSZMMnEv0e4ZAjBomBLGt6/oodBN4EEKFko0IC z7lNnU1chyMq5++BG9oppW4tU35qUGbM70e7vW5R2VenZeVNle7WRMV9PM7aoCll9FDyToggtFh y3nM1tyfxmnPcmhkmr6Arv/MeRImecDofJlbA8Gq1/NTHBdFh5h7VJz33oSPSRmR4KNJajQwru0 oV6bvQm+LM2rktW39ya9RNbnqonExofCyI0arK6BQ3PYO4mcSczuAwRcMy9ABCKxBGIs9zpXCoo aXWaEhK33clY8pQ== 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 unsigned 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 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: Alexander Viro Cc: Christian Brauner Cc: Jan Kara Cc: linux-fsdevel@vger.kernel.org Signed-off-by: Kees Cook Reviewed-by: Jan Kara --- fs/read_write.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/fs/read_write.c b/fs/read_write.c index d4c036e82b6c..e24b94a8937d 100644 --- a/fs/read_write.c +++ b/fs/read_write.c @@ -1417,6 +1417,7 @@ static int generic_copy_file_checks(struct file *file_in, loff_t pos_in, struct inode *inode_out = file_inode(file_out); uint64_t count = *req_count; loff_t size_in; + loff_t sum_in, sum_out; int ret; ret = generic_file_rw_checks(file_in, file_out); @@ -1451,7 +1452,8 @@ static int generic_copy_file_checks(struct file *file_in, loff_t pos_in, return -ETXTBSY; /* Ensure offsets don't wrap. */ - if (pos_in + count < pos_in || pos_out + count < pos_out) + if (check_add_overflow(pos_in, count, &sum_in) || + check_add_overflow(pos_out, count, &sum_out)) return -EOVERFLOW; /* Shorten the copy to EOF */ @@ -1467,8 +1469,8 @@ static int generic_copy_file_checks(struct file *file_in, loff_t pos_in, /* Don't allow overlapped copying within the same file. */ if (inode_in == inode_out && - pos_out + count > pos_in && - pos_out < pos_in + count) + sum_out > pos_in && + pos_out < sum_in) return -EINVAL; *req_count = count;