Messages in this thread | | | Date | Wed, 17 Mar 2021 15:20:35 -0700 | From | Kees Cook <> | Subject | Re: [RESEND PATCH v2 2/2] pstore: Add buffer start check during init |
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On Thu, Feb 25, 2021 at 09:30:17PM +0530, Mukesh Ojha wrote: > From: Huang Yiwei <hyiwei@codeaurora.org> > > In a scenario of panic, when we use DRAM to store log instead > of persistant storage and during warm reset when we copy these > data outside of ram. Missing check on prz->start(write position) > can cause crash because it can be any value and can point outside > the mapped region. So add the start check to avoid. > > Signed-off-by: Huang Yiwei <hyiwei@codeaurora.org> > Signed-off-by: Mukesh Ojha <mojha@codeaurora.org> > --- > change in v2: > - this is on top of first patchset. > > fs/pstore/ram_core.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c > index 0da012f..a15748a 100644 > --- a/fs/pstore/ram_core.c > +++ b/fs/pstore/ram_core.c > @@ -514,7 +514,7 @@ static int persistent_ram_post_init(struct persistent_ram_zone *prz, u32 sig, > sig ^= PERSISTENT_RAM_SIG; > > if (prz->buffer->sig == sig) { > - if (buffer_size(prz) == 0) { > + if (buffer_size(prz) == 0 && buffer_start(prz) == 0) { > pr_debug("found existing empty buffer\n"); > return 0;
Were you seeing cases where the sig was correct, size was zero and start was non-zero but still smaller than buffer_size(prz)?
That should only happen if a prz changed in size (but not location) across boots, and I guess, yes, should be detected and zapped. But that means you need a case for size=0 buffer_start!=0 for zapping.
But you talk about a crash without this test? "any value" isn't true, the next tests make sure it's within buffer_size:
if (buffer_size(prz) > prz->buffer_size || buffer_start(prz) > buffer_size(prz)) { pr_info("found existing invalid buffer, size %zu, start %zu\n", buffer_size(prz), buffer_start(prz)); zap = true;
can you tell me more about what you're seeing?
-Kees
-- Kees Cook
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