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bpf: don't prune branches when a scalar is replaced with a pointer

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From: Jann Horn <jannh@google.com>

[ Upstream commit 179d1c5602 ]

This could be made safe by passing through a reference to env and checking
for env->allow_ptr_leaks, but it would only work one way and is probably
not worth the hassle - not doing it will not directly lead to program
rejection.

Fixes: f1174f77b5 ("bpf/verifier: rework value tracking")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Daniel Borkmann 2017-12-22 16:23:10 +01:00 committed by Greg Kroah-Hartman
parent c90268f7cb
commit cb56cc1b29
1 changed files with 7 additions and 8 deletions
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15
kernel/bpf/verifier.c
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@ -3337,15 +3337,14 @@ static bool regsafe(struct bpf_reg_state *rold, struct bpf_reg_state *rcur,
return range_within(rold, rcur) &&
tnum_in(rold->var_off, rcur->var_off);
} else {
/* if we knew anything about the old value, we're not
* equal, because we can't know anything about the
* scalar value of the pointer in the new value.
/* We're trying to use a pointer in place of a scalar.
* Even if the scalar was unbounded, this could lead to
* pointer leaks because scalars are allowed to leak
* while pointers are not. We could make this safe in
* special cases if root is calling us, but it's
* probably not worth the hassle.
*/
return rold->umin_value == 0 &&
rold->umax_value == U64_MAX &&
rold->smin_value == S64_MIN &&
rold->smax_value == S64_MAX &&
tnum_is_unknown(rold->var_off);
return false;
}
case PTR_TO_MAP_VALUE:
/* If the new min/max/var_off satisfy the old ones and