This is a note to let you know that I've just added the patch titled
libbpf: Fix realloc API handling in zero-sized edge cases
to the 6.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
libbpf-fix-realloc-api-handling-in-zero-sized-edge-c.patch
and it can be found in the queue-6.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit a855ce58027086dcdaf9f514d5cde6ca2da838a0
Author: Andrii Nakryiko <andrii@xxxxxxxxxx>
Date: Mon Jul 10 19:41:50 2023 -0700
libbpf: Fix realloc API handling in zero-sized edge cases
[ Upstream commit 8a0260dbf6553c969248b6530cafadac46562f47 ]
realloc() and reallocarray() can either return NULL or a special
non-NULL pointer, if their size argument is zero. This requires a bit
more care to handle NULL-as-valid-result situation differently from
NULL-as-error case. This has caused real issues before ([0]), and just
recently bit again in production when performing bpf_program__attach_usdt().
This patch fixes 4 places that do or potentially could suffer from this
mishandling of NULL, including the reported USDT-related one.
There are many other places where realloc()/reallocarray() is used and
NULL is always treated as an error value, but all those have guarantees
that their size is always non-zero, so those spot don't need any extra
handling.
[0] d08ab82f59d5 ("libbpf: Fix double-free when linker processes empty sections")
Fixes: 999783c8bbda ("libbpf: Wire up spec management and other arch-independent USDT logic")
Fixes: b63b3c490eee ("libbpf: Add bpf_program__set_insns function")
Fixes: 697f104db8a6 ("libbpf: Support custom SEC() handlers")
Fixes: b12688267280 ("libbpf: Change the order of data and text relocations.")
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/bpf/20230711024150.1566433-1-andrii@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 57c040a9c3705..2a4dbe7d9b3d4 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -6136,7 +6136,11 @@ static int append_subprog_relos(struct bpf_program *main_prog, struct bpf_progra
if (main_prog == subprog)
return 0;
relos = libbpf_reallocarray(main_prog->reloc_desc, new_cnt, sizeof(*relos));
- if (!relos)
+ /* if new count is zero, reallocarray can return a valid NULL result;
+ * in this case the previous pointer will be freed, so we *have to*
+ * reassign old pointer to the new value (even if it's NULL)
+ */
+ if (!relos && new_cnt)
return -ENOMEM;
if (subprog->nr_reloc)
memcpy(relos + main_prog->nr_reloc, subprog->reloc_desc,
@@ -8504,7 +8508,8 @@ int bpf_program__set_insns(struct bpf_program *prog,
return -EBUSY;
insns = libbpf_reallocarray(prog->insns, new_insn_cnt, sizeof(*insns));
- if (!insns) {
+ /* NULL is a valid return from reallocarray if the new count is zero */
+ if (!insns && new_insn_cnt) {
pr_warn("prog '%s': failed to realloc prog code\n", prog->name);
return -ENOMEM;
}
@@ -8813,7 +8818,11 @@ int libbpf_unregister_prog_handler(int handler_id)
/* try to shrink the array, but it's ok if we couldn't */
sec_defs = libbpf_reallocarray(custom_sec_defs, custom_sec_def_cnt, sizeof(*sec_defs));
- if (sec_defs)
+ /* if new count is zero, reallocarray can return a valid NULL result;
+ * in this case the previous pointer will be freed, so we *have to*
+ * reassign old pointer to the new value (even if it's NULL)
+ */
+ if (sec_defs || custom_sec_def_cnt == 0)
custom_sec_defs = sec_defs;
return 0;
diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c
index 086eef355ab3d..1af77f9935833 100644
--- a/tools/lib/bpf/usdt.c
+++ b/tools/lib/bpf/usdt.c
@@ -852,8 +852,11 @@ static int bpf_link_usdt_detach(struct bpf_link *link)
* system is so exhausted on memory, it's the least of user's
* concerns, probably.
* So just do our best here to return those IDs to usdt_manager.
+ * Another edge case when we can legitimately get NULL is when
+ * new_cnt is zero, which can happen in some edge cases, so we
+ * need to be careful about that.
*/
- if (new_free_ids) {
+ if (new_free_ids || new_cnt == 0) {
memcpy(new_free_ids + man->free_spec_cnt, usdt_link->spec_ids,
usdt_link->spec_cnt * sizeof(*usdt_link->spec_ids));
man->free_spec_ids = new_free_ids;
