From aba8520b1e43d85f52431251232f96384e704cb5 Mon Sep 17 00:00:00 2001 From: Mark Wielaard Date: Sun, 21 Jan 2024 20:54:39 +0100 Subject: [PATCH] libdwfl: Add some extra space to buffer to read kernel image header MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit GCC 14 notices we play some tricks with the array into which we try to read the kernel image header. image-header.c: In function ‘__libdw_image_header’: image-header.c:77:18: error: array subscript -496 is outside array bounds of ‘char[96]’ [-Werror=array-bounds=] 77 | header = header_buffer - H_START; | ^ image-header.c:67:12: note: at offset -496 into object ‘header_buffer’ of size 96 67 | char header_buffer[H_READ_SIZE]; | ^~~~~~~~~~~~~ GCC is correct. The new header pointer is before the actually buffer we want to read from. Later in the code we "correct" the address again by adding the "offset" off the elements we want to read. Such pointer arithmetic is technically invalid. Make it valid by making the buffer a little bigger, so all pointer arithmetic stays inside the header_buffer. This does waste 496 bytes on the stack at the front of the buffer that is never used. * libdwfl/image-header.c (__libdw_image_header): Add H_START to header_buffer size and return Signed-off-by: Mark Wielaard --- libdwfl/image-header.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/libdwfl/image-header.c b/libdwfl/image-header.c index c777cc849..03cd7a761 100644 --- a/libdwfl/image-header.c +++ b/libdwfl/image-header.c @@ -1,6 +1,6 @@ /* Linux kernel image support for libdwfl. Copyright (C) 2009-2011 Red Hat, Inc. - Copyright (C) 2022 Mark J. Wielaard + Copyright (C) 2022, 2024 Mark J. Wielaard This file is part of elfutils. This file is free software; you can redistribute it and/or modify @@ -64,17 +64,17 @@ __libdw_image_header (int fd, off_t *start_offset, if (likely (mapped_size > H_END)) { const void *header = mapped; - char header_buffer[H_READ_SIZE]; + char header_buffer[H_READ_SIZE + H_START]; if (header == NULL) { - ssize_t n = pread_retry (fd, header_buffer, H_READ_SIZE, + ssize_t n = pread_retry (fd, header_buffer + H_START, H_READ_SIZE, *start_offset + H_START); if (n < 0) return DWFL_E_ERRNO; if (n < H_READ_SIZE) return DWFL_E_BADELF; - header = header_buffer - H_START; + header = header_buffer; } uint16_t magic1; -- 2.47.2