diff mbox series

[v3,bpf-next,01/10] lib/buildid: harden build ID parsing logic

Message ID 20240730203914.1182569-2-andrii@kernel.org (mailing list archive)
State New
Headers show
Series Harden and extend ELF build ID parsing logic | expand

Commit Message

Andrii Nakryiko July 30, 2024, 8:39 p.m. UTC 
Harden build ID parsing logic, adding explicit READ_ONCE() where it's
important to have a consistent value read and validated just once.

Fixes tag below points to the code that moved this code into
lib/buildid.c, and then subsequently was used in perf subsystem, making
this code exposed to perf_event_open() users in v5.12+.

Cc: stable@vger.kernel.org
Cc: Jann Horn <jannh@google.com>
Suggested-by: Andi Kleen <ak@linux.intel.com>
Fixes: bd7525dacd7e ("bpf: Move stack_map_get_build_id into lib")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 lib/buildid.c | 51 +++++++++++++++++++++++++++------------------------
 1 file changed, 27 insertions(+), 24 deletions(-)

Comments

Andi Kleen July 31, 2024, 4:04 a.m. UTC | #1 
>  	while (note_offs + sizeof(Elf32_Nhdr) < note_size) {
>  		Elf32_Nhdr *nhdr = (Elf32_Nhdr *)(note_start + note_offs);
>  
> +		name_sz = READ_ONCE(nhdr->n_namesz);
> +		desc_sz = READ_ONCE(nhdr->n_descsz);
>  		if (nhdr->n_type == BUILD_ID &&
> -		    nhdr->n_namesz == sizeof("GNU") &&
> -		    !strcmp((char *)(nhdr + 1), "GNU") &&
> -		    nhdr->n_descsz > 0 &&
> -		    nhdr->n_descsz <= BUILD_ID_SIZE_MAX) {
> -			memcpy(build_id,
> -			       note_start + note_offs +
> -			       ALIGN(sizeof("GNU"), 4) + sizeof(Elf32_Nhdr),
> -			       nhdr->n_descsz);
> -			memset(build_id + nhdr->n_descsz, 0,
> -			       BUILD_ID_SIZE_MAX - nhdr->n_descsz);
> +		    name_sz == note_name_sz &&
> +		    strcmp((char *)(nhdr + 1), note_name) == 0 &&

Doesn't the strcmp need a boundary check to be inside note_size too?

Other it may read into the next page, which could be unmapped, causing a fault.
Given it's unlikely that this happen, and the end has guard pages,
but there are some users of set_memory_np.

You could just move the later checks earlier.

The rest looks good to me.

-Andi
Andrii Nakryiko July 31, 2024, 9:54 p.m. UTC | #2 
On Tue, Jul 30, 2024 at 9:05 PM Andi Kleen <ak@linux.intel.com> wrote:
>
> >       while (note_offs + sizeof(Elf32_Nhdr) < note_size) {
> >               Elf32_Nhdr *nhdr = (Elf32_Nhdr *)(note_start + note_offs);
> >
> > +             name_sz = READ_ONCE(nhdr->n_namesz);
> > +             desc_sz = READ_ONCE(nhdr->n_descsz);
> >               if (nhdr->n_type == BUILD_ID &&
> > -                 nhdr->n_namesz == sizeof("GNU") &&
> > -                 !strcmp((char *)(nhdr + 1), "GNU") &&
> > -                 nhdr->n_descsz > 0 &&
> > -                 nhdr->n_descsz <= BUILD_ID_SIZE_MAX) {
> > -                     memcpy(build_id,
> > -                            note_start + note_offs +
> > -                            ALIGN(sizeof("GNU"), 4) + sizeof(Elf32_Nhdr),
> > -                            nhdr->n_descsz);
> > -                     memset(build_id + nhdr->n_descsz, 0,
> > -                            BUILD_ID_SIZE_MAX - nhdr->n_descsz);
> > +                 name_sz == note_name_sz &&
> > +                 strcmp((char *)(nhdr + 1), note_name) == 0 &&
>
> Doesn't the strcmp need a boundary check to be inside note_size too?
>
> Other it may read into the next page, which could be unmapped, causing a fault.
> Given it's unlikely that this happen, and the end has guard pages,
> but there are some users of set_memory_np.
>
> You could just move the later checks earlier.

Yep, good catch! I'll move the overflow check and will add a note_size
check to it, thanks!

>
> The rest looks good to me.
>
> -Andi
>
diff mbox series

Patch

diff --git a/lib/buildid.c b/lib/buildid.c
index e02b5507418b..d21d86f6c19a 100644
--- a/lib/buildid.c
+++ b/lib/buildid.c
@@ -18,28 +18,29 @@  static int parse_build_id_buf(unsigned char *build_id,
 			      const void *note_start,
 			      Elf32_Word note_size)
 {
+	const char note_name[] = "GNU";
+	const size_t note_name_sz = sizeof(note_name);
 	Elf32_Word note_offs = 0, new_offs;
+	u32 name_sz, desc_sz;
+	const char *data;
 
 	while (note_offs + sizeof(Elf32_Nhdr) < note_size) {
 		Elf32_Nhdr *nhdr = (Elf32_Nhdr *)(note_start + note_offs);
 
+		name_sz = READ_ONCE(nhdr->n_namesz);
+		desc_sz = READ_ONCE(nhdr->n_descsz);
 		if (nhdr->n_type == BUILD_ID &&
-		    nhdr->n_namesz == sizeof("GNU") &&
-		    !strcmp((char *)(nhdr + 1), "GNU") &&
-		    nhdr->n_descsz > 0 &&
-		    nhdr->n_descsz <= BUILD_ID_SIZE_MAX) {
-			memcpy(build_id,
-			       note_start + note_offs +
-			       ALIGN(sizeof("GNU"), 4) + sizeof(Elf32_Nhdr),
-			       nhdr->n_descsz);
-			memset(build_id + nhdr->n_descsz, 0,
-			       BUILD_ID_SIZE_MAX - nhdr->n_descsz);
+		    name_sz == note_name_sz &&
+		    strcmp((char *)(nhdr + 1), note_name) == 0 &&
+		    desc_sz > 0 && desc_sz <= BUILD_ID_SIZE_MAX) {
+			data = note_start + note_offs + ALIGN(note_name_sz, 4);
+			memcpy(build_id, data, desc_sz);
+			memset(build_id + desc_sz, 0, BUILD_ID_SIZE_MAX - desc_sz);
 			if (size)
-				*size = nhdr->n_descsz;
+				*size = desc_sz;
 			return 0;
 		}
-		new_offs = note_offs + sizeof(Elf32_Nhdr) +
-			ALIGN(nhdr->n_namesz, 4) + ALIGN(nhdr->n_descsz, 4);
+		new_offs = note_offs + sizeof(Elf32_Nhdr) + ALIGN(name_sz, 4) + ALIGN(desc_sz, 4);
 		if (new_offs <= note_offs)  /* overflow */
 			break;
 		note_offs = new_offs;
@@ -71,7 +72,7 @@  static int get_build_id_32(const void *page_addr, unsigned char *build_id,
 {
 	Elf32_Ehdr *ehdr = (Elf32_Ehdr *)page_addr;
 	Elf32_Phdr *phdr;
-	int i;
+	__u32 i, phnum;
 
 	/*
 	 * FIXME
@@ -80,9 +81,10 @@  static int get_build_id_32(const void *page_addr, unsigned char *build_id,
 	 */
 	if (ehdr->e_phoff != sizeof(Elf32_Ehdr))
 		return -EINVAL;
+
+	phnum = READ_ONCE(ehdr->e_phnum);
 	/* only supports phdr that fits in one page */
-	if (ehdr->e_phnum >
-	    (PAGE_SIZE - sizeof(Elf32_Ehdr)) / sizeof(Elf32_Phdr))
+	if (phnum > (PAGE_SIZE - sizeof(Elf32_Ehdr)) / sizeof(Elf32_Phdr))
 		return -EINVAL;
 
 	phdr = (Elf32_Phdr *)(page_addr + sizeof(Elf32_Ehdr));
@@ -90,8 +92,8 @@  static int get_build_id_32(const void *page_addr, unsigned char *build_id,
 	for (i = 0; i < ehdr->e_phnum; ++i) {
 		if (phdr[i].p_type == PT_NOTE &&
 		    !parse_build_id(page_addr, build_id, size,
-				    page_addr + phdr[i].p_offset,
-				    phdr[i].p_filesz))
+				    page_addr + READ_ONCE(phdr[i].p_offset),
+				    READ_ONCE(phdr[i].p_filesz)))
 			return 0;
 	}
 	return -EINVAL;
@@ -103,7 +105,7 @@  static int get_build_id_64(const void *page_addr, unsigned char *build_id,
 {
 	Elf64_Ehdr *ehdr = (Elf64_Ehdr *)page_addr;
 	Elf64_Phdr *phdr;
-	int i;
+	__u32 i, phnum;
 
 	/*
 	 * FIXME
@@ -112,18 +114,19 @@  static int get_build_id_64(const void *page_addr, unsigned char *build_id,
 	 */
 	if (ehdr->e_phoff != sizeof(Elf64_Ehdr))
 		return -EINVAL;
+
+	phnum = READ_ONCE(ehdr->e_phnum);
 	/* only supports phdr that fits in one page */
-	if (ehdr->e_phnum >
-	    (PAGE_SIZE - sizeof(Elf64_Ehdr)) / sizeof(Elf64_Phdr))
+	if (phnum > (PAGE_SIZE - sizeof(Elf64_Ehdr)) / sizeof(Elf64_Phdr))
 		return -EINVAL;
 
 	phdr = (Elf64_Phdr *)(page_addr + sizeof(Elf64_Ehdr));
 
-	for (i = 0; i < ehdr->e_phnum; ++i) {
+	for (i = 0; i < phnum; ++i) {
 		if (phdr[i].p_type == PT_NOTE &&
 		    !parse_build_id(page_addr, build_id, size,
-				    page_addr + phdr[i].p_offset,
-				    phdr[i].p_filesz))
+				    page_addr + READ_ONCE(phdr[i].p_offset),
+				    READ_ONCE(phdr[i].p_filesz)))
 			return 0;
 	}
 	return -EINVAL;