Messages in this thread | | | From | He Fengqing <> | Subject | Re: [bpf-next 3/3] bpf: Fix a use after free in bpf_check() | Date | Thu, 8 Jul 2021 11:00:39 +0800 |
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在 2021/7/7 15:25, Song Liu 写道: > On Tue, Jul 6, 2021 at 8:53 PM He Fengqing <hefengqing@huawei.com> wrote: >> >> In bpf_patch_insn_data, env->prog was input parameter of >> bpf_patch_insn_single function. bpf_patch_insn_single call >> bpf_prog_realloc to realloc ebpf prog. When we need to malloc new prog, >> bpf_prog_realloc will free the old prog, in this scenery is the >> env->prog. >> Then bpf_patch_insn_data function call adjust_insn_aux_data function, if >> adjust_insn_aux_data function return error, bpf_patch_insn_data will >> return NULL. >> In bpf_check->convert_ctx_accesses->bpf_patch_insn_data call chain, if >> bpf_patch_insn_data return NULL, env->prog has been freed in >> bpf_prog_realloc, then bpf_check will use the freed env->prog. > > Besides "what is the bug", please also describe "how to fix it". For example, > add "Fix it by adding a free_old argument to bpf_prog_realloc(), and ...". > Also, for the subject of 0/3, it is better to say "fix potential > memory leak and ...".
Thanks for your suggestion.
> >> >> Signed-off-by: He Fengqing <hefengqing@huawei.com> >> --- >> include/linux/filter.h | 2 +- >> kernel/bpf/core.c | 9 ++++--- >> kernel/bpf/verifier.c | 53 ++++++++++++++++++++++++++++++++---------- >> net/core/filter.c | 2 +- >> 4 files changed, 49 insertions(+), 17 deletions(-) >> >> diff --git a/include/linux/filter.h b/include/linux/filter.h >> index f39e008a377d..ec11a5ae92c2 100644 >> --- a/include/linux/filter.h >> +++ b/include/linux/filter.h >> @@ -881,7 +881,7 @@ void bpf_prog_jit_attempt_done(struct bpf_prog *prog); >> struct bpf_prog *bpf_prog_alloc(unsigned int size, gfp_t gfp_extra_flags); >> struct bpf_prog *bpf_prog_alloc_no_stats(unsigned int size, gfp_t gfp_extra_flags); >> struct bpf_prog *bpf_prog_realloc(struct bpf_prog *fp_old, unsigned int size, >> - gfp_t gfp_extra_flags); >> + gfp_t gfp_extra_flags, bool free_old); >> void __bpf_prog_free(struct bpf_prog *fp); >> >> static inline void bpf_prog_clone_free(struct bpf_prog *fp) >> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c >> index 49b0311f48c1..e5616bb1665b 100644 >> --- a/kernel/bpf/core.c >> +++ b/kernel/bpf/core.c >> @@ -218,7 +218,7 @@ void bpf_prog_fill_jited_linfo(struct bpf_prog *prog, >> } >> >> struct bpf_prog *bpf_prog_realloc(struct bpf_prog *fp_old, unsigned int size, >> - gfp_t gfp_extra_flags) >> + gfp_t gfp_extra_flags, bool free_old) >> { >> gfp_t gfp_flags = GFP_KERNEL_ACCOUNT | __GFP_ZERO | gfp_extra_flags; >> struct bpf_prog *fp; >> @@ -238,7 +238,8 @@ struct bpf_prog *bpf_prog_realloc(struct bpf_prog *fp_old, unsigned int size, >> /* We keep fp->aux from fp_old around in the new >> * reallocated structure. >> */ >> - bpf_prog_clone_free(fp_old); >> + if (free_old) >> + bpf_prog_clone_free(fp_old); >> } >> >> return fp; >> @@ -456,7 +457,7 @@ struct bpf_prog *bpf_patch_insn_single(struct bpf_prog *prog, u32 off, >> * last page could have large enough tailroom. >> */ >> prog_adj = bpf_prog_realloc(prog, bpf_prog_size(insn_adj_cnt), >> - GFP_USER); >> + GFP_USER, false); >> if (!prog_adj) >> return ERR_PTR(-ENOMEM); >> >> @@ -1150,6 +1151,8 @@ struct bpf_prog *bpf_jit_blind_constants(struct bpf_prog *prog) >> return tmp; >> } >> >> + if (tmp != clone) >> + bpf_prog_clone_free(clone); >> clone = tmp; >> insn_delta = rewritten - 1; >> >> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c >> index 41109f49b724..e75b933f69e4 100644 >> --- a/kernel/bpf/verifier.c >> +++ b/kernel/bpf/verifier.c >> @@ -11855,7 +11855,10 @@ static int opt_subreg_zext_lo32_rnd_hi32(struct bpf_verifier_env *env, >> new_prog = bpf_patch_insn_data(env, adj_idx, patch, patch_len); >> if (!new_prog) >> return -ENOMEM; >> - env->prog = new_prog; >> + if (new_prog != env->prog) { >> + bpf_prog_clone_free(env->prog); >> + env->prog = new_prog; >> + } > > Can we move this check into bpf_patch_insn_data()?
Ok, I will change this in next version.
> >> insns = new_prog->insnsi; >> aux = env->insn_aux_data; >> delta += patch_len - 1; > [...] > >> diff --git a/net/core/filter.c b/net/core/filter.c >> index d70187ce851b..8a8d1a3ba5c2 100644 >> --- a/net/core/filter.c >> +++ b/net/core/filter.c >> @@ -1268,7 +1268,7 @@ static struct bpf_prog *bpf_migrate_filter(struct bpf_prog *fp) >> >> /* Expand fp for appending the new filter representation. */ >> old_fp = fp; >> - fp = bpf_prog_realloc(old_fp, bpf_prog_size(new_len), 0); >> + fp = bpf_prog_realloc(old_fp, bpf_prog_size(new_len), 0, true); > > Can we add some logic here and not add free_old to bpf_prog_realloc()?
Ok, maybe we can free old_fp here, never in bpf_prog_realloc.
> > Thanks, > Song > . >
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