[PATCH v5 bpf-next 01/10] lib/buildid: harden build ID parsing logic

Andrii Nakryiko
2024-08-13T00:29:42Z

Harden build ID parsing logic, adding explicit READ_ONCE() where it's
important to have a consistent value read and validated just once.

Also, as pointed out by Andi Kleen, we need to make sure that entire ELF
note is within a page bounds, so move the overflow check up and add an
extra note_size boundaries validation.

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 | 74 ++++++++++++++++++++++++++++++---------------------
1 file changed, 43 insertions(+), 31 deletions(-)

diff --git a/lib/buildid.c b/lib/buildid.c
index e02b5507418b..61bc5b767064 100644
--- a/lib/buildid.c
+++ b/lib/buildid.c
@@ -18,31 +18,37 @@ static int parse_build_id_buf(unsigned char *build_id,
const void *note_start,
Elf32_Word note_size)
{
- Elf32_Word note_offs = 0, new_offs;
-
- while (note_offs + sizeof(Elf32_Nhdr) < note_size) {
- Elf32_Nhdr *nhdr = (Elf32_Nhdr *)(note_start + note_offs);
+ const char note_name[] = "GNU";
+ const size_t note_name_sz = sizeof(note_name);
+ u64 note_off = 0, new_off, name_sz, desc_sz;
+ const char *data;
+
+ while (note_off + sizeof(Elf32_Nhdr) < note_size &&
+ note_off + sizeof(Elf32_Nhdr) > note_off /* overflow */) {
+ Elf32_Nhdr *nhdr = (Elf32_Nhdr *)(note_start + note_off);
+
+ name_sz = READ_ONCE(nhdr->n_namesz);
+ desc_sz = READ_ONCE(nhdr->n_descsz);
+
+ new_off = note_off + sizeof(Elf32_Nhdr);
+ if (check_add_overflow(new_off, ALIGN(name_sz, 4), &new_off) ||
+ check_add_overflow(new_off, ALIGN(desc_sz, 4), &new_off) ||
+ new_off > note_size)
+ break;

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_off + 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);
- if (new_offs <= note_offs) /* overflow */
- break;
- note_offs = new_offs;
+
+ note_off = new_off;
}

return -EINVAL;
@@ -71,7 +77,7 @@ 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 +86,10 @@ 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 +97,8 @@ 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 +110,7 @@ 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 +119,19 @@ 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;
@@ -152,6 +160,10 @@ int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id,
page = find_get_page(vma->vm_file->f_mapping, 0);
if (!page)
return -EFAULT; /* page not mapped */
+ if (!PageUptodate(page)) {
+ put_page(page);
+ return -EFAULT;
+ }

ret = -EINVAL;
page_addr = kmap_local_page(page);
--
2.43.5