6.4-stable review patch. If anyone has any objections, please let me know.
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From: Andrii Nakryiko andrii@kernel.org
[ 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@kernel.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net Link: https://lore.kernel.org/bpf/20230711024150.1566433-1-andrii@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- tools/lib/bpf/libbpf.c | 15 ++++++++++++--- tools/lib/bpf/usdt.c | 5 ++++- 2 files changed, 16 insertions(+), 4 deletions(-)
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;