cbfstool: elfheaders: use common checks and buffer helpers

The elfheaders code was manipulating struct buffers. Use
the introduced buffer helper functions. Additionally fix
up offset and size checks for the program headers and section
headers by using common code paths.

Change-Id: I279c77f77aaa1860a0be43fb111df890dd1d84d5
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/5368
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: Marc Jones <marc.jones@se-eng.com>

1 files changed, 79 insertions, 68 deletions

diff --git a/util/cbfstool/elfheaders.c b/util/cbfstool/elfheaders.c
index 0d874a1171..78c864fa52 100644
--- a/util/cbfstool/elfheaders.c
+++ b/util/cbfstool/elfheaders.c
@@ -128,12 +128,25 @@
 static void
 elf_eident(struct buffer *input, Elf64_Ehdr *ehdr)
 {
-	memmove(ehdr->e_ident, input->data, sizeof(ehdr->e_ident));
-	input->data += sizeof(ehdr->e_ident);
-	input->size -= sizeof(ehdr->e_ident);
+	bgets(input, ehdr->e_ident, sizeof(ehdr->e_ident));
 }
 
 
+static int
+check_size(const struct buffer *b, size_t offset, size_t size, const char *desc)
+{
+	if (size == 0)
+		return 0;
+
+	if (offset >= buffer_size(b) || (offset + size) > buffer_size(b)) {
+		ERROR("The file is not large enough for the '%s'. "
+		      "%ld bytes @ offset %zu, input %zu bytes.\n",
+		      desc, size, offset, buffer_size(b));
+		return -1;
+	}
+	return 0;
+}
+
 static void
 elf_ehdr(struct buffer *input, Elf64_Ehdr *ehdr, struct xdr *xdr, int bit64)
 {
@@ -169,7 +182,8 @@ elf_phdr(struct buffer *pinput, Elf64_Phdr *phdr,
 	 * pointer the full entsize; rather than get tricky
 	 * we just advance it below.
 	 */
-	struct buffer input = *pinput;
+	struct buffer input;
+	buffer_clone(&input, pinput);
 	if (bit64){
 		phdr->p_type = xdr->get32(&input);
 		phdr->p_flags = xdr->get32(&input);
@@ -189,8 +203,7 @@ elf_phdr(struct buffer *pinput, Elf64_Phdr *phdr,
 		phdr->p_flags = xdr->get32(&input);
 		phdr->p_align = xdr->get32(&input);
 	}
-	pinput->size -= entsize;
-	pinput->data += entsize;
+	buffer_seek(pinput, entsize);
 }
 
 static void
@@ -228,8 +241,58 @@ elf_shdr(struct buffer *pinput, Elf64_Shdr *shdr,
 		shdr->sh_addralign = xdr->get32(&input);
 		shdr->sh_entsize = xdr->get32(&input);
 	}
-	pinput->size -= entsize;
-	pinput->data += entsize;
+	buffer_seek(pinput, entsize);
+}
+
+static Elf64_Phdr *
+phdr_read(const struct buffer *in, Elf64_Ehdr *ehdr, struct xdr *xdr, int bit64)
+{
+	struct buffer b;
+	Elf64_Phdr *phdr;
+	int i;
+
+	/* cons up an input buffer for the headers.
+	 * Note that the program headers can be anywhere,
+	 * per the ELF spec, You'd be surprised how many ELF
+	 * readers miss this little detail.
+	 */
+	buffer_splice(&b, in, ehdr->e_phoff, ehdr->e_phentsize * ehdr->e_phnum);
+	if (check_size(in, ehdr->e_phoff, buffer_size(&b), "program headers"))
+		return NULL;
+
+	/* gather up all the phdrs.
+	 * We do them all at once because there is more
+	 * than one loop over all the phdrs.
+	 */
+	phdr = calloc(sizeof(*phdr), ehdr->e_phnum);
+	for (i = 0; i < ehdr->e_phnum; i++)
+		elf_phdr(&b, &phdr[i], ehdr->e_phentsize, xdr, bit64);
+
+	return phdr;
+}
+
+static Elf64_Shdr *
+shdr_read(const struct buffer *in, Elf64_Ehdr *ehdr, struct xdr *xdr, int bit64)
+{
+	struct buffer b;
+	Elf64_Shdr *shdr;
+	int i;
+
+	/* cons up an input buffer for the section headers.
+	 * Note that the section headers can be anywhere,
+	 * per the ELF spec, You'd be surprised how many ELF
+	 * readers miss this little detail.
+	 */
+	buffer_splice(&b, in, ehdr->e_shoff, ehdr->e_shentsize * ehdr->e_shnum);
+	if (check_size(in, ehdr->e_shoff, buffer_size(&b), "section headers"))
+		return NULL;
+
+	/* gather up all the shdrs. */
+	shdr = calloc(sizeof(*shdr), ehdr->e_shnum);
+	for (i = 0; i < ehdr->e_shnum; i++)
+		elf_shdr(&b, &shdr[i], ehdr->e_shentsize, xdr, bit64);
+
+	return shdr;
 }
 
 /* Get the headers from the buffer.
@@ -246,16 +309,13 @@ elf_headers(const struct buffer *pinput,
 	    Elf64_Phdr **pphdr,
 	    Elf64_Shdr **pshdr)
 {
-	int i;
 	struct xdr *xdr = &xdr_le;
 	int bit64 = 0;
-	struct buffer input = *(struct buffer *)pinput;
-	struct buffer phdr_buf;
-	struct buffer shdr_buf;
-	Elf64_Phdr *phdr;
-	Elf64_Shdr *shdr;
+	struct buffer input;
+
+	buffer_clone(&input, pinput);
 
-	if (!iself((unsigned char *)pinput->data)) {
+	if (!iself(buffer_get(pinput))) {
 		ERROR("The stage file is not in ELF format!\n");
 		return -1;
 	}
@@ -280,65 +340,16 @@ elf_headers(const struct buffer *pinput,
 		return -1;
 	}
 
-	if (pinput->size < ehdr->e_phoff){
-		ERROR("The program header offset is greater than "
-		      "the remaining file size."
-		      "%ld bytes left, program header offset is %ld \n",
-		      pinput->size, ehdr->e_phoff);
+	*pphdr = phdr_read(pinput, ehdr, xdr, bit64);
+	if (*pphdr == NULL)
 		return -1;
-	}
-	/* cons up an input buffer for the headers.
-	 * Note that the program headers can be anywhere,
-	 * per the ELF spec, You'd be surprised how many ELF
-	 * readers miss this little detail.
-	 */
-	phdr_buf.data = &pinput->data[ehdr->e_phoff];
-	phdr_buf.size = ehdr->e_phentsize * ehdr->e_phnum;
-	if (phdr_buf.size > (pinput->size - ehdr->e_phoff)){
-		ERROR("The file is not large enough for the program headers."
-		      "%ld bytes left, %ld bytes of headers\n",
-		      pinput->size - ehdr->e_phoff, phdr_buf.size);
-		return -1;
-	}
-	/* gather up all the phdrs.
-	 * We do them all at once because there is more
-	 * than one loop over all the phdrs.
-	 */
-	phdr = calloc(sizeof(*phdr), ehdr->e_phnum);
-	for (i = 0; i < ehdr->e_phnum; i++)
-		elf_phdr(&phdr_buf, &phdr[i], ehdr->e_phentsize, xdr, bit64);
-	*pphdr = phdr;
 
 	if (!pshdr)
 		return 0;
 
-	if (pinput->size < ehdr->e_shoff){
-		ERROR("The section header offset is greater than "
-		      "the remaining file size."
-		      "%ld bytes left, program header offset is %ld \n",
-		      pinput->size, ehdr->e_shoff);
-		return -1;
-	}
-	/* cons up an input buffer for the section headers.
-	 * Note that the section headers can be anywhere,
-	 * per the ELF spec, You'd be surprised how many ELF
-	 * readers miss this little detail.
-	 */
-	shdr_buf.data = &pinput->data[ehdr->e_shoff];
-	shdr_buf.size = ehdr->e_shentsize * ehdr->e_shnum;
-	if (shdr_buf.size > (pinput->size - ehdr->e_shoff)){
-		ERROR("The file is not large enough for the section headers."
-		      "%ld bytes left, %ld bytes of headers\n",
-		      pinput->size - ehdr->e_shoff, shdr_buf.size);
+	*pshdr = shdr_read(pinput, ehdr, xdr, bit64);
+	if (*pshdr == NULL)
 		return -1;
-	}
-	/* gather up all the shdrs. */
-
-	shdr = calloc(sizeof(*shdr), ehdr->e_shnum);
-	for (i = 0; i < ehdr->e_shnum; i++)
-		elf_shdr(&shdr_buf, &shdr[i], ehdr->e_shentsize, xdr, bit64);
-	*pshdr = shdr;
 
 	return 0;
 }
-