From 8bea4a83aac0cb888ca72af9b823d4b68f40696e Mon Sep 17 00:00:00 2001 From: Andreas Rheinhardt Date: Sun, 6 Aug 2023 08:40:13 +0200 Subject: [PATCH] avutil/bprint: Allow size == 0 in av_bprint_init_for_buffer() The AVBPrint API guarantees that the string buffer is always zero-terminated; in order to honour this guarantee, there obviously must be a string buffer at all and it must have a size >= 1. Therefore av_bprint_init_for_buffer() treats passing a NULL buffer or size == 0 as invalid data that leads to undefined behaviour, namely NPD in case NULL is provided or a write to a buffer of size 0 in case size == 0. But it would be easy to support this, namely by using the internal buffer with AV_BPRINT_SIZE_COUNT_ONLY in case size == 0. There is a reason to allow this: Several functions like av_channel_(description|name) are actually wrappers around corresponding AVBPrint functions. They accept user provided buffers and are supposed to return the required size of the buffer, which would allow the user to call it once to get the required buffer size and call it once more after having allocated the buffer. If av_bprint_init_for_buffer() treats size == 0 as invalid, all these users would need to check for this themselves and basically add the same codeblock that this patch adds to av_bprint_init_for_buffer(). This change is in line with e.g. snprintf() which also allows the pointer to be NULL in case size is zero. This fixes Coverity issues #1503074, #1503076 and #1503082; all of these issues are about providing NULL to the channel-layout functions that are wrappers around AVBPrint versions. Reviewed-by: Nicolas George Signed-off-by: Andreas Rheinhardt --- libavutil/bprint.c | 5 +++++ libavutil/bprint.h | 3 +++ libavutil/version.h | 2 +- 3 files changed, 9 insertions(+), 1 deletion(-) diff --git a/libavutil/bprint.c b/libavutil/bprint.c index 23998a8b02..4e9571715c 100644 --- a/libavutil/bprint.c +++ b/libavutil/bprint.c @@ -84,6 +84,11 @@ void av_bprint_init(AVBPrint *buf, unsigned size_init, unsigned size_max) void av_bprint_init_for_buffer(AVBPrint *buf, char *buffer, unsigned size) { + if (size == 0) { + av_bprint_init(buf, 0, AV_BPRINT_SIZE_COUNT_ONLY); + return; + } + buf->str = buffer; buf->len = 0; buf->size = size; diff --git a/libavutil/bprint.h b/libavutil/bprint.h index f27d30f723..8559745478 100644 --- a/libavutil/bprint.h +++ b/libavutil/bprint.h @@ -144,6 +144,9 @@ void av_bprint_init(AVBPrint *buf, unsigned size_init, unsigned size_max); * Init a print buffer using a pre-existing buffer. * * The buffer will not be reallocated. + * In case size equals zero, the AVBPrint will be initialized to use + * the internal buffer as if using AV_BPRINT_SIZE_COUNT_ONLY with + * av_bprint_init(). * * @param buf buffer structure to init * @param buffer byte buffer to use for the string data diff --git a/libavutil/version.h b/libavutil/version.h index 9e798b0e3f..b36310ee4c 100644 --- a/libavutil/version.h +++ b/libavutil/version.h @@ -79,7 +79,7 @@ */ #define LIBAVUTIL_VERSION_MAJOR 58 -#define LIBAVUTIL_VERSION_MINOR 15 +#define LIBAVUTIL_VERSION_MINOR 16 #define LIBAVUTIL_VERSION_MICRO 100 #define LIBAVUTIL_VERSION_INT AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \