On Thu, 10 Sep 2026 00:40:55 +0000
[email protected] wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s)
> to consider:
>
> Pre-existing issues:
> - [High] Incomplete Fix / Integer Truncation Leading to Heap Overflow
> --
>
> commit 2d027c4ee8625f17122dea0afb65c1e4b21ae531
> Author: Masami Hiramatsu (Google) <[email protected]>
>
> tools/bootconfig: Fix integer overflow in size check
>
> This commit modifies the size check in load_xbc_from_initrd() to prevent
> an integer overflow on 32-bit systems. It changes the condition to
> subtract BOOTCONFIG_FOOTER_SIZE from stat.st_size instead of adding it
> to the bootconfig size.
>
> Closes:
> https://lore.kernel.org/all/[email protected]/
>
> > diff --git a/tools/bootconfig/main.c b/tools/bootconfig/main.c
> > index 7dc9fff9b6370..b380ad6777faa 100644
> > --- a/tools/bootconfig/main.c
> > +++ b/tools/bootconfig/main.c
> > @@ -218,7 +218,7 @@ static int load_xbc_from_initrd(int fd, char **buf)
> > csum = le32toh(csum);
> >
> > /* Wrong size error */
> > - if (stat.st_size < size + BOOTCONFIG_FOOTER_SIZE) {
> > + if (size > stat.st_size - BOOTCONFIG_FOOTER_SIZE) {
>
> [Severity: High]
> This is a pre-existing issue, but the fix doesn't seem to completely resolve
> the integer truncation and heap overflow vulnerabilities.
>
> Can this size check still be bypassed for large files? Since stat.st_size is a
> 64-bit off_t, if the file size is larger than 4.29 GB, stat.st_size -
> BOOTCONFIG_FOOTER_SIZE can exceed UINT32_MAX. A corrupted uint32_t size of
> 0xFFFFFFFF would bypass this check because it is always smaller than the
> right side.
>
> If bypassed, does passing 0xFFFFFFFF to load_xbc_fd() cause an integer
> truncation and heap overflow?
>
> tools/bootconfig/main.c:load_xbc_fd() {
> ...
> static int load_xbc_fd(int fd, char **buf, int size)
> ...
> *buf = malloc(size + 1);
> if (!*buf)
> return -ENOMEM;
>
> ret = read(fd, *buf, size);
> ...
> (*buf)[size] = '\0';
> ...
> }
>
> Because size is an int, 0xFFFFFFFF is truncated to -1. This results in
> malloc(0) which returns a valid heap chunk. The read() call then receives -1
> which gets cast to SIZE_MAX, overflowing the heap chunk. Finally, a null byte
> is written to a negative array index (-1), causing an out-of-bounds write.
This part should be fixed in v2. But below is another problem.
>
> Does this same vulnerability also affect load_xbc_file() when processing
> standalone files >= 2GB?
>
> tools/bootconfig/main.c:load_xbc_file() {
> ...
> ret = fstat(fd, &stat);
> ...
> ret = load_xbc_fd(fd, buf, stat.st_size);
> ...
> }
>
> This implicitly truncates the 64-bit off_t stat.st_size into the 32-bit int
> size parameter of load_xbc_fd().
>
> > pr_err("bootconfig size is too big\n");
> > return -E2BIG;
> > }
OK, let me update the patch.
Thank you,
--
Masami Hiramatsu (Google) <[email protected]>
