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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id fr23sm6380245pjb.22.2021.04.01.15.13.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Apr 2021 15:13:29 -0700 (PDT) From: Kees Cook To: Greg Kroah-Hartman Cc: Kees Cook , Arnd Bergmann , Christoph Hellwig , Nathan Chancellor , Tejun Heo , Alexander Viro , "Rafael J. Wysocki" , Shuah Khan , Nathan Chancellor , Nick Desaulniers , Andrew Morton , Kefeng Wang , "Matthew Wilcox (Oracle)" , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, clang-built-linux@googlegroups.com, Michal Hocko , Alexey Dobriyan , Lee Duncan , Chris Leech , Adam Nichols , linux-hardening@vger.kernel.org Subject: [PATCH v4 2/3] seq_file: Fix clang warning for NULL pointer arithmetic Date: Thu, 1 Apr 2021 15:13:19 -0700 Message-Id: <20210401221320.2717732-3-keescook@chromium.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210401221320.2717732-1-keescook@chromium.org> References: <20210401221320.2717732-1-keescook@chromium.org> MIME-Version: 1.0 X-Patch-Hashes: v=1; h=sha256; g=072ba8d0292080bbec63f540b8a7b8f4388d46e0; i=X28+TLSj6UAzyfUwM6ASBpL0O+6znj4kpkRLU6W477w=; m=BVZ7UGjppHc9pxpbNOtE+k2Mc/TPPXIP/bm3a5RPhjA=; p=bMQkNyH1GTm6eEjiE8Zl6RhCNwohxteBG+pqB7gCs1I= X-Patch-Sig: m=pgp; i=arnd@arndb.de; s=0x0x8972F4DFDC6DC026; b=iQIzBAABCgAdFiEEpcP2jyKd1g9yPm4TiXL039xtwCYFAmBmRX8ACgkQiXL039xtwCaLMg/+Lhx pOKAP38pEErrYMo+5DOvXlMaNUoctJ8O82UArlKz1tK0WnGh/2r6wsUb57mBRxiEm1Fqs4js4duAl kR7kxnB0PYJgEVpDX2mbErnsMYYEpTK2OPrFPfuXpogkv7ZzBTR8dfQwxETzu+yBfjnn1DmRNqIVF j9TrK2uBIE7lwsIWWyEuuEVYoZ68xhrJ9IrQ1ZLE5fA4VF/woqhbJKXQAUimIgUO6mvg9OJpISbWs CYQxi2njTOqAtu8mSsyhsuBuW8KV+G/PeM0oSqythjF6LKzULC86d3WEH6aEazn2znU7/frImFMxl UhkTHmOfkr/tMJyxO8jDuPjpXytP0fmIkpOSgNIh7PlQgLWXf5+OkbCoU/WSTY1jR27M7+HAvGd7Q C9hYO6odGUvbXgyGVaruHYEZfTQ/1Mym/duFmytroX4JG8bnj5gVv9L01vETRRa9WSeP6Fj8vzxoA ko6fy/Oq77nJ2SiA//Z1h3wNCzGagcTHRAh96xkDD1FzytY3Hjb8tbTwBZsYvlmvjQnyscKPBUPHc N8EC5Bc7vZPFKzPf53UMw/NirSq1etb50K5J7aWmAbmgJm+qryafE51E/Xvd/uaOrzjdypKRhuxGN uCHmvLBr6U1WaTio88kV78F55LIb9pgl0iVP+4UV7wscGidMpLzJGIVSeO8qaN5w= Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Arnd Bergmann Clang points out that adding something to NULL is not allowed in standard C: fs/kernfs/file.c:127:15: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic] return NULL + !*ppos; ~~~~ ^ fs/seq_file.c:529:14: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic] return NULL + (*pos == 0); Rephrase the code to be extra explicit about the valid, giving them named SEQ_OPEN_EOF and SEQ_OPEN_SINGLE definitions. The instance in kernfs was copied from single_start, so fix both at once. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Fixes: c2b19daf6760 ("sysfs, kernfs: prepare read path for kernfs") Reviewed-by: Christoph Hellwig Reviewed-by: Nathan Chancellor Signed-off-by: Arnd Bergmann Signed-off-by: Kees Cook Link: https://lore.kernel.org/r/20201028151202.3074398-1-arnd@kernel.org --- fs/kernfs/file.c | 9 ++++++--- fs/seq_file.c | 5 ++++- include/linux/seq_file.h | 6 ++++++ 3 files changed, 16 insertions(+), 4 deletions(-) diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c index c75719312147..721bcbc1d4d0 100644 --- a/fs/kernfs/file.c +++ b/fs/kernfs/file.c @@ -122,10 +122,13 @@ static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos) return next; } else { /* - * The same behavior and code as single_open(). Returns - * !NULL if pos is at the beginning; otherwise, NULL. + * The same behavior and code as single_open(). Continues + * if pos is at the beginning; otherwise, NULL. */ - return NULL + !*ppos; + if (*ppos) + return NULL; + + return SEQ_OPEN_SINGLE; } } diff --git a/fs/seq_file.c b/fs/seq_file.c index cb11a34fb871..1b5bd95d0a48 100644 --- a/fs/seq_file.c +++ b/fs/seq_file.c @@ -542,7 +542,10 @@ EXPORT_SYMBOL(seq_dentry); static void *single_start(struct seq_file *p, loff_t *pos) { - return NULL + (*pos == 0); + if (*pos) + return NULL; + + return SEQ_OPEN_SINGLE; } static void *single_next(struct seq_file *p, void *v, loff_t *pos) diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h index b83b3ae3c877..51c870765bfd 100644 --- a/include/linux/seq_file.h +++ b/include/linux/seq_file.h @@ -37,6 +37,12 @@ struct seq_operations { #define SEQ_SKIP 1 +/* + * op->start must return a non-NULL pointer for single_open(), + * this is used when we don't care about the specific value. + */ +#define SEQ_OPEN_SINGLE ((void *)1) + /** * seq_has_overflowed - check if the buffer has overflowed * @m: the seq_file handle -- 2.25.1