Messages in this thread | | | Date | Fri, 4 Aug 2023 09:53:11 -0700 | From | Kees Cook <> | Subject | Re: [PATCH 1/1] pstore/ram: Check member of buffers during the initialization phase of the pstore |
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On Fri, Aug 04, 2023 at 04:59:07PM +0800, yunlong xing wrote: > On Fri, Aug 4, 2023 at 4:10 PM Kees Cook <keescook@chromium.org> wrote: > > > > On Tue, Aug 01, 2023 at 02:04:32PM +0800, Yunlong Xing wrote: > > > From: Enlin Mu <enlin.mu@unisoc.com> > > > > > > The commit 30696378f68a("pstore/ram: Do not treat empty buffers as valid") > > > would introduce the following issue: > > > > > > When finding the buffer_size is zero, it would return directly.However, at > > > the same time, if the buffer's start is a illegal value, the others would > > > panic if access the buffer. > > > > Which "others" do you mean? > > About “others", You can refer to the following panic call stack: > sysdump_panic_event+0x720/0xd38 > atomic_notifier_call_chain+0x58/0xc0 > panic+0x1c4/0x6e4 > die+0x3c0/0x428 > bug_handler+0x4c/0x9c > brk_handler+0x98/0x14c > do_debug_exception+0x114/0x2ec > el1_dbg+0x18/0xbc > usercopy_abort+0x90/0x94 > __check_object_size+0x17c/0x2c4 > persistent_ram_update_user+0x50/0x220 > persistent_ram_write_user+0x354/0x428 > ramoops_pstore_write_user+0x34/0x50 > write_pmsg+0x14c/0x26c
I see -- the "start" is corrupted and out of bounds, which leads to these accesses.
> do_iter_write+0x1cc/0x2cc > vfs_writev+0xf4/0x168 > do_writev+0xa4/0x200 > __arm64_sys_writev+0x20/0x2c > el0_svc_common+0xc8/0x22c > el0_svc_handler+0x1c/0x28 > el0_svc+0x8/0x100 > > > > > To avoid these happenning, check if the members are legal during the > > > initialization phase of the pstore. > > > > > > Fixes: 30696378f68a ("pstore/ram: Do not treat empty buffers as valid") > > > Cc: stable@vger.kernel.org > > > Signed-off-by: Enlin Mu <enlin.mu@unisoc.com> > > > --- > > > 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 85aaf0fc6d7d..eb6df190d752 100644 > > > --- a/fs/pstore/ram_core.c > > > +++ b/fs/pstore/ram_core.c > > > @@ -519,7 +519,7 @@ 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; > > > } > > > > And in the case of "buffer_size(prz) == 0" but "buffer_start(prz) != 0", > > this will be caught by: > > > > 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; > > } > > > > i.e. it will be detected and zapped back to a sane state. > No,This code has no chance of execution because there was a return 0 before it
Right, I meant the behavior with your patch -- with your patch the case of "size == 0 && start != 0" would be caught by the above check ("start > size") and zapped back to sanity. (Which is the correct result.)
> > > > That sounds correct to me, though I wonder if reporting it as an > > "invalid buffer" is inaccurate? Perhaps we should have a separate case: > > > > if (buffer_size(prz) == 0) { > > if (buffer_start(prz) == 0) > > pr_debug("found existing empty buffer\n"); > > else { > > pr_debug("found existing empty buffer with non-zero start\n"); > > zap = true; > > } > > } else if ... > > > > What do you think? > Good, I gree it. For me, it should not return directly while finding > the buffer_size is zero, We need Check others case.
Right. The only question I have is: how did the "start" get corrupted, and is that a notable condition? Right now we don't (info-level) log a size==0 prz since that's an expected state for a regular initialized prz. So maybe your patch is correct as-is since we'd want to report the "found existing invalid buffer" case.
> So does the modification method you mentioned require me to resubmit a > patch or do you need to modify and merge it
I think I'll update the commit log and take this as-is. If the logging becomes too noisy, we can adjust the case later.
Thanks!
-- Kees Cook
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