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([2a0a:ef40:724:6601:f3ff:aebc:61f8:d91f]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a199e5db12sm347118375e9.2.2026.10.14.04.38.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 14 Oct 2026 04:38:02 -0700 (PDT) Message-ID: <96c1d112-1b05-4663-90c6-33374dccd764@gmail.com> Date: Wed, 14 Oct 2026 12:37:59 +0100 Precedence: bulk X-Mailing-List: git@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: phillip.wood@dunelm.org.uk Subject: Re: [PATCH 3/5] wrapper: reject insanely large byte counts when reading/writing To: Johannes Schindelin via GitGitGadget , git@vger.kernel.org Cc: Johannes Schindelin , "Randall S. Becker" References: Content-Language: en-US From: Phillip Wood In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi Johannes On 14/10/2026 07:09, Johannes Schindelin via GitGitGadget wrote: > From: Johannes Schindelin > > Both the `read_in_full()` as well as the `write_in_full()` function > accumulate the bytes transferred count in a variable of type `ssize_t`, > but accept a `size_t` count parameter. When count exceeds `SSIZE_MAX`, > that total count overflows after processing `SSIZE_MAX` bytes, producing > a negative return value that callers interpret as an error (or worse, a > small positive value after further wrapping). > > In practice, git never passes such large counts because file sizes and > buffer allocations are bounded well below SSIZE_MAX on all target > platforms. Are we sure about that? In the past we've had bug fixes such as c14e5a1a50 (transport-helper: use xread instead of read, 2019-01-03) on platforms where ssize_t is narrower that size_t (POSIX does not require them to be the same width). I've cc'd Randall to see if ssize_t is still narrower than size_t on the NonStop platforms git supports. Thanks Phillip > The POSIX specification for `read()` and `write()` also > limits single operations to `SSIZE_MAX` bytes, and git's > `xread()`/`xwrite()` wrappers further clamp to `MAX_IO_SIZE`. But the > accumulation in the `*_in_full()` wrappers means that even with per-call > clamping, total can exceed `SSIZE_MAX` when count does. > > Reject a total count that exceeds the range of `ssize_t` upfront with > `EINVAL` rather than silently producing wrong return values, matching > the POSIX convention for invalid arguments. > > Pointed out by Coverity. > > Assisted-by: Claude Opus 4.6 > Signed-off-by: Johannes Schindelin > --- > git-compat-util.h | 4 ++++ > wrapper.c | 10 ++++++++++ > 2 files changed, 14 insertions(+) > > diff --git a/git-compat-util.h b/git-compat-util.h > index a0f901ce79..afce8b85b8 100644 > --- a/git-compat-util.h > +++ b/git-compat-util.h > @@ -740,6 +740,10 @@ static inline uint64_t u64_add(uint64_t a, uint64_t b) > */ > #define DEFAULT_IO_BUFFER_SIZE (128 * 1024) > > +#ifndef SSIZE_MAX > +# define SSIZE_MAX ((ssize_t)(((size_t)-1) >> 1)) > +#endif > + > #ifdef HAVE_ALLOCA_H > # include > # define xalloca(size) (alloca(size)) > diff --git a/wrapper.c b/wrapper.c > index 05a9cd369c..ea9c14f834 100644 > --- a/wrapper.c > +++ b/wrapper.c > @@ -288,6 +288,11 @@ ssize_t read_in_full(int fd, void *buf, size_t count) > char *p = buf; > ssize_t total = 0; > > + if (count > SSIZE_MAX) { > + errno = EINVAL; > + return -1; > + } > + > while (count > 0) { > ssize_t loaded = xread(fd, p, count); > if (loaded < 0) > @@ -307,6 +312,11 @@ ssize_t write_in_full(int fd, const void *buf, size_t count) > const char *p = buf; > ssize_t total = 0; > > + if (count > SSIZE_MAX) { > + errno = EINVAL; > + return -1; > + } > + > while (count > 0) { > ssize_t written = xwrite(fd, p, count); > if (written < 0)