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| author | Roland McGrath <roland@redhat.com> | 2009-02-06 17:34:07 -0800 |
|---|---|---|
| committer | Roland McGrath <roland@redhat.com> | 2009-02-06 17:34:07 -0800 |
| commit | 92dc07b1f988e8c237a38e23be660b9b8533e6fd (patch) | |
| tree | 4a689fbb465d7302b105678152170d8665f56ae7 | |
| parent | 6cec50838ed04a9833fb5549f698d3756bbe7e72 (diff) | |
| download | lwn-92dc07b1f988e8c237a38e23be660b9b8533e6fd.tar.gz lwn-92dc07b1f988e8c237a38e23be660b9b8533e6fd.zip | |
elf core dump: fix get_user use
The elf_core_dump() code does its work with set_fs(KERNEL_DS) in force,
so vma_dump_size() needs to switch back with set_fs(USER_DS) to safely
use get_user() for a normal user-space address.
Checking for VM_READ optimizes out the case where get_user() would fail
anyway. The vm_file check here was already superfluous given the control
flow earlier in the function, so that is a cleanup/optimization unrelated
to other changes but an obvious and trivial one.
Reported-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Roland McGrath <roland@redhat.com>
| -rw-r--r-- | fs/binfmt_elf.c | 14 |
1 files changed, 12 insertions, 2 deletions
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c index e3ff2b9e602f..33b7235f853b 100644 --- a/fs/binfmt_elf.c +++ b/fs/binfmt_elf.c @@ -1208,9 +1208,11 @@ static unsigned long vma_dump_size(struct vm_area_struct *vma, * check for an ELF header. If we find one, dump the first page to * aid in determining what was mapped here. */ - if (FILTER(ELF_HEADERS) && vma->vm_file != NULL && vma->vm_pgoff == 0) { + if (FILTER(ELF_HEADERS) && + vma->vm_pgoff == 0 && (vma->vm_flags & VM_READ)) { u32 __user *header = (u32 __user *) vma->vm_start; u32 word; + mm_segment_t fs = get_fs(); /* * Doing it this way gets the constant folded by GCC. */ @@ -1223,7 +1225,15 @@ static unsigned long vma_dump_size(struct vm_area_struct *vma, magic.elfmag[EI_MAG1] = ELFMAG1; magic.elfmag[EI_MAG2] = ELFMAG2; magic.elfmag[EI_MAG3] = ELFMAG3; - if (get_user(word, header) == 0 && word == magic.cmp) + /* + * Switch to the user "segment" for get_user(), + * then put back what elf_core_dump() had in place. + */ + set_fs(USER_DS); + if (unlikely(get_user(word, header))) + word = 0; + set_fs(fs); + if (word == magic.cmp) return PAGE_SIZE; } |