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linux-user: Fix signed math overflow in brk() syscall

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Fix the math overflow when calculating the new_malloc_size.

new_host_brk_page and brk_page are unsigned integers. If userspace
reduces the heap, new_host_brk_page is lower than brk_page which results
in a huge positive number (but should actually be negative).

Fix it by adding a proper check and as such make the code more readable.

Signed-off-by: Helge Deller <deller@gmx.de>
Tested-by: "Markus F.X.J. Oberhumer" <markus@oberhumer.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Fixes: 86f04735ac ("linux-user: Fix brk() to release pages")
Cc: qemu-stable@nongnu.org
Buglink: https://github.com/upx/upx/issues/683
This commit is contained in:
Helge Deller 2023-07-17 12:39:38 +02:00
parent dfe49864af
commit eac78a4b0b
1 changed files with 3 additions and 2 deletions
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5
linux-user/syscall.c
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@ -860,12 +860,13 @@ abi_long do_brk(abi_ulong brk_val)
* itself); instead we treat "mapped but at wrong address" as
* a failure and unmap again.
*/
new_alloc_size = new_host_brk_page - brk_page;
if (new_alloc_size) {
if (new_host_brk_page > brk_page) {
new_alloc_size = new_host_brk_page - brk_page;
mapped_addr = get_errno(target_mmap(brk_page, new_alloc_size,
PROT_READ|PROT_WRITE,
MAP_ANON|MAP_PRIVATE, 0, 0));
} else {
new_alloc_size = 0;
mapped_addr = brk_page;
}