6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Masami Hiramatsu (Google) [ Upstream commit 7812d6dab0698001e50e8c2f901e17da3eb6f429 ] 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: de462e5f1071 ("bootconfig: Fix to remove bootconfig data from initrd while boot") Cc: stable@vger.kernel.org Reported-by: Sashiko Closes: https://lore.kernel.org/all/20260910010137.EE0431F000FF@smtp.kernel.org/ Assisted-by: Antigravity:gemini-3.8-flash Signed-off-by: Masami Hiramatsu (Google) Reviewed-by: Sang-Heon Jeon Signed-off-by: Sasha Levin --- init/main.c | 25 +++++++++++++++---------- 1 file changed, 15 insertions(+), 10 deletions(-) diff --git a/init/main.c b/init/main.c index 62d8f7610e846..1442f95d6da10 100644 --- a/init/main.c +++ b/init/main.c @@ -268,7 +268,8 @@ static void * __init get_boot_config_from_initrd(size_t *_size) u32 *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; @@ -285,16 +286,26 @@ static void * __init get_boot_config_from_initrd(size_t *_size) found: hdr = (u32 *)(data - 8); + if ((unsigned long)hdr < initrd_start) + return NULL; + size = le32_to_cpu(hdr[0]); csum = le32_to_cpu(hdr[1]); - 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; @@ -397,12 +408,6 @@ 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) -- 2.53.0