[PATCH] lib/bug: ignore non-allocated module bug tables

[Laxman Acharya Padhya]

rewrite_section_headers() initially sets sh_addr for every section to its
address in the temporary module image. Only SHF_ALLOC sections are later
copied to module memory and have sh_addr updated.

module_bug_finalize() accepts any section named __bug_table. A malformed
module can therefore leave mod->bug_table pointing into the temporary
image, which is freed after loading. A later BUG/WARN lookup would then
scan freed memory.

Require the bug table section to be allocated before retaining its
address. Valid modules are unchanged because __bug_table is allocated.

Fixes: 7664c5a1da47 ("[PATCH] Generic BUG implementation")
Signed-off-by: Laxman Acharya Padhya <acharyalaxman8848@xxxxxxxxx>
---
 lib/bug.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/bug.c b/lib/bug.c
index 7c1c2c27f..44966ead1 100644
--- a/lib/bug.c
+++ b/lib/bug.c
@@ -94,7 +94,8 @@ void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
 	/* Find the __bug_table section, if present */
 	secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
 	for (i = 1; i < hdr->e_shnum; i++) {
-		if (strcmp(secstrings+sechdrs[i].sh_name, "__bug_table"))
+		if (strcmp(secstrings + sechdrs[i].sh_name, "__bug_table") ||
+		    !(sechdrs[i].sh_flags & SHF_ALLOC))
 			continue;
 		mod->bug_table = (void *) sechdrs[i].sh_addr;
 		mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry);
-- 
2.51.2