Messages in this thread | | | From | "Pearson, Greg" <> | Subject | Re: [PATCH v2] vmcore: prevent PT_NOTE p_memsz overflow during header update | Date | Mon, 3 Feb 2014 22:57:58 +0000 |
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On 02/03/2014 02:38 PM, Vivek Goyal wrote: > On Mon, Feb 03, 2014 at 01:18:38PM -0700, Greg Pearson wrote: > > [..] >> diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c >> index 2ca7ba0..051c803 100644 >> --- a/fs/proc/vmcore.c >> +++ b/fs/proc/vmcore.c >> @@ -468,12 +468,14 @@ static int __init update_note_header_size_elf64(const Elf64_Ehdr *ehdr_ptr) >> return rc; >> } >> nhdr_ptr = notes_section; >> - while (real_sz < max_sz) { >> - if (nhdr_ptr->n_namesz == 0) >> - break; >> + while (nhdr_ptr->n_namesz != 0) { >> sz = sizeof(Elf64_Nhdr) + >> ((nhdr_ptr->n_namesz + 3) & ~3) + >> ((nhdr_ptr->n_descsz + 3) & ~3); >> + if ((real_sz + sz) > max_sz) { >> + pr_warn("Warning: dropping PT_NOTE entry\n"); >> + break; >> + } > Hi Greg, > > Couple of minor nits. > > I think it is a good idea to give more data in warning which tells why > are we dropping a note entry. May be something like. > > "Warning: Total note entry size exceeded PT_NOTE memsz. Dropping PT_NOTE entry, n_namesz=<> n_descsz=<>".
Sounds good I'll add more information to the pr_warn().
> > Secondly, if there is only on note entry in a PT_NOTE header and we drop > it, then that PT_NOTE header is empty and needs to be cleaned up. > > I think you will have to modify get_note_number_and_size_elf64() and > other relevant functions which are not expecting ->p_memsz=0.
What about treating this as an error condition and adding a check to the update_note_header_size_elf32()/update_note_header_size_elf64() routines that would return a failure, something like the following at the end of the routine:
if (real_sz == 0) return -EINVAL
I could also add a pr_warn() with a message indicating no PT_NOTE entries were found.
This seems like a lower risk change to handle the case I'm currently seeing as opposed to changing the code to handle a p_memsz==0.
Thoughts?
-- Greg
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