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bootconfig: Fix integer overflow in initrd size check

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Sashiko reported that in get_boot_config_from_initrd(), a crafted initrd
with a huge bootconfig size (such as 0xFFFFFFFF) can cause the pointer
arithmetic:

    data = ((void *)hdr) - size;

to wrap around on 32-bit systems (or when pointer subtraction overflows).
Because data wraps around, the subsequent bounds check:

    if ((unsigned long)data < initrd_start)

evaluates to false, bypassing the check. The kernel then calls
xbc_calc_checksum(data, size), which attempts to read 4GB of memory,
hitting unmapped pages and triggering a fatal kernel page fault during
early boot. Furthermore, on 64-bit systems with an initrd > 4.29 GB, an
unbounded 32-bit size can similarly bypass the initrd_start check.

Fix this by:
1. Ensuring the initrd is at least large enough to contain the bootconfig
   footer and verifying hdr is within the initrd bounds.
2. Checking that size does not exceed XBC_DATA_MAX and does not exceed
   the available space between initrd_start and hdr before performing
   pointer subtraction.

Link: https://lore.kernel.org/all/178905333479.213925.1358412668943562406.stgit@devnote2/

Fixes: de462e5f10 ("bootconfig: Fix to remove bootconfig data from initrd while boot")
Cc: stable@vger.kernel.org
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://lore.kernel.org/all/20260910010137.EE0431F000FF@smtp.kernel.org/
Assisted-by: Antigravity:gemini-3.8-flash
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Sang-Heon Jeon <ekffu200098@gmail.com>
This commit is contained in:
Masami Hiramatsu (Google)
2026-09-11 23:06:10 +09:00
parent 462d0b066b
commit 7812d6dab0
1 changed files with 15 additions and 10 deletions
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init/main.c
+15 -10
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@@ -277,7 +277,8 @@ static void * __init get_boot_config_from_initrd(size_t *_size)
u8 *hdr;
int i;
if (!initrd_end)
if (!initrd_end || initrd_end < initrd_start ||
initrd_end - initrd_start < BOOTCONFIG_MAGIC_LEN + 8)
return NULL;
data = (char *)initrd_end - BOOTCONFIG_MAGIC_LEN;
@@ -294,16 +295,26 @@ static void * __init get_boot_config_from_initrd(size_t *_size)
found:
hdr = (u8 *)(data - 8);
if ((unsigned long)hdr < initrd_start)
return NULL;
size = get_unaligned_le32(hdr);
csum = get_unaligned_le32(hdr + 4);
data = ((void *)hdr) - size;
if ((unsigned long)data < initrd_start) {
pr_err("bootconfig size %d is greater than initrd size %ld\n",
if (size > XBC_DATA_MAX) {
pr_err("bootconfig size %u is greater than max size %d\n",
size, XBC_DATA_MAX);
return NULL;
}
if (size > ((unsigned long)hdr - initrd_start)) {
pr_err("bootconfig size %u is greater than initrd size %lu\n",
size, initrd_end - initrd_start);
return NULL;
}
data = ((void *)hdr) - size;
if (xbc_calc_checksum(data, size) != csum) {
pr_err("bootconfig checksum failed\n");
return NULL;
@@ -394,12 +405,6 @@ static void __init setup_boot_config(void)
return;
}
if (size >= XBC_DATA_MAX) {
pr_err("bootconfig size %ld greater than max size %d\n",
(long)size, XBC_DATA_MAX);
return;
}
ret = xbc_init(data, size, &msg, &pos);
if (ret < 0) {
if (pos < 0)