From: Masami Hiramatsu (Google) <[email protected]>
Sashiko reported that on 32-bit systems, if an attacker crafts size in
the bootconfig footer such that adding BOOTCONFIG_FOOTER_SIZE wraps around
(for instance, if size is 0xFFFFFFFF), the size check in
load_xbc_from_initrd() can be bypassed:
if (stat.st_size < size + BOOTCONFIG_FOOTER_SIZE) {
pr_err("bootconfig size is too big\n");
return -E2BIG;
}
Furthermore, on 64-bit systems with an initrd > 4.29 GB, comparing a
corrupted 32-bit size (e.g. 0xFFFFFFFF) against
stat.st_size - BOOTCONFIG_FOOTER_SIZE can also bypass the check if
size is not bounded. Similarly, load_xbc_file() passes 64-bit stat.st_size
directly into the 32-bit int size parameter of load_xbc_fd(), truncating
large standalone files (>= 2GB).
In both cases, passing 0xFFFFFFFF to load_xbc_fd() truncates to -1,
resulting in malloc(0), an integer overflow in read(), and an
out-of-bounds null-byte write.
Fix this by:
1. Rejecting size > XBC_DATA_MAX or
size > stat.st_size - BOOTCONFIG_FOOTER_SIZE in load_xbc_from_initrd().
2. Rejecting stat.st_size > XBC_DATA_MAX in load_xbc_file() before passing
it to load_xbc_fd().
3. Checking size < 0 || size > XBC_DATA_MAX defensively in load_xbc_fd().
Fixes: 950313ebf79c ("tools: bootconfig: Add bootconfig command")
Cc: [email protected]
Reported-by: Sashiko <[email protected]>
Closes: https://lore.kernel.org/all/[email protected]/
Closes: https://lore.kernel.org/all/[email protected]/
Assisted-by: Antigravity:gemini-3.8-flash
Signed-off-by: Masami Hiramatsu (Google) <[email protected]>
---
Changes in v3:
- Reject size > XBC_DATA_MAX and
size > stat.st_size - BOOTCONFIG_FOOTER_SIZE in load_xbc_from_initrd()
to prevent bypass on initrd > 4.29 GB.
- Check stat.st_size > XBC_DATA_MAX in load_xbc_file() to prevent
truncation on large standalone files.
- Check size < 0 || size > XBC_DATA_MAX defensively in load_xbc_fd().
Changes in v2:
- Add Cc: stable.
- Also reject if "size > XBC_DATA_MAX", that is obviously wrong.
---
tools/bootconfig/main.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/tools/bootconfig/main.c b/tools/bootconfig/main.c
index 7dc9fff9b637..17d971d47f87 100644
--- a/tools/bootconfig/main.c
+++ b/tools/bootconfig/main.c
@@ -140,6 +140,9 @@ static int load_xbc_fd(int fd, char **buf, int size)
{
int ret;
+ if (size < 0 || size > XBC_DATA_MAX)
+ return -EINVAL;
+
*buf = malloc(size + 1);
if (!*buf)
return -ENOMEM;
@@ -168,6 +171,13 @@ static int load_xbc_file(const char *path, char **buf)
return ret;
}
+ if (stat.st_size > XBC_DATA_MAX) {
+ pr_err("%s size is too big\n", path);
+ ret = -E2BIG;
+ close(fd);
+ return ret;
+ }
+
ret = load_xbc_fd(fd, buf, stat.st_size);
close(fd);
@@ -218,7 +228,8 @@ 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 > XBC_DATA_MAX ||
+ size > stat.st_size - BOOTCONFIG_FOOTER_SIZE) {
pr_err("bootconfig size is too big\n");
return -E2BIG;
}
