lib/buildid: don't limit .note.gnu.build-id to the first page in ELF

With freader we don't need to restrict ourselves to a single page, so
let's allow ELF notes to be at any valid position with the file.

We also merge parse_build_id() and parse_build_id_buf() as now the only
difference between them is note offset overflow, which makes sense to
check in all situations.

Reviewed-by: Eduard Zingerman <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: anakryiko

lib/buildid.c

@@ -155,17 +155,18 @@ static void freader_cleanup(struct freader *r)
  * 32-bit and 64-bit system, because Elf32_Nhdr and Elf64_Nhdr are
  * identical.
  */
-static int parse_build_id_buf(struct freader *r,
-			      unsigned char *build_id, __u32 *size,
-			      loff_t note_off, Elf32_Word note_size)
+static int parse_build_id(struct freader *r, unsigned char *build_id, __u32 *size,
+			  loff_t note_off, Elf32_Word note_size)
 {
 	const char note_name[] = "GNU";
 	const size_t note_name_sz = sizeof(note_name);
 	u32 build_id_off, new_off, note_end, name_sz, desc_sz;
 	const Elf32_Nhdr *nhdr;
 	const char *data;
 
-	note_end = note_off + note_size;
+	if (check_add_overflow(note_off, note_size, &note_end))
+		return -EINVAL;
+
 	while (note_end - note_off > sizeof(Elf32_Nhdr) + note_name_sz) {
 		nhdr = freader_fetch(r, note_off, sizeof(Elf32_Nhdr) + note_name_sz);
 		if (!nhdr)
@@ -204,23 +205,6 @@ static int parse_build_id_buf(struct freader *r,
 	return -EINVAL;
 }
 
-static inline int parse_build_id(struct freader *r,
-				 unsigned char *build_id,
-				 __u32 *size,
-				 loff_t note_start_off,
-				 Elf32_Word note_size)
-{
-	/* check for overflow */
-	if (note_start_off + note_size < note_start_off)
-		return -EINVAL;
-
-	/* only supports note that fits in the first page */
-	if (note_start_off + note_size > PAGE_SIZE)
-		return -EINVAL;
-
-	return parse_build_id_buf(r, build_id, size, note_start_off, note_size);
-}
-
 /* Parse build ID from 32-bit ELF */
 static int get_build_id_32(struct freader *r, unsigned char *build_id, __u32 *size)
 {