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libbpf: Fix realloc API handling in zero-sized edge cases

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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@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20230711024150.1566433-1-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko
2023-07-10 19:41:50 -07:00
committed by Andrii Nakryiko
parent 6c020e6c47
commit f117080307
2 changed files with 16 additions and 4 deletions
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5
src/usdt.c
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@@ -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;