[patch 36/56] elf core dump: fix get_user use

Greg KH
2009-02-11T00:41:00Z

[-- Attachment #1: elf-core-dump-fix-get_user-use.patch --]
[-- Type: text/plain, Size: 1968 bytes --]

2.6.27-stable review patch. If anyone has any objections, please let us know.
------------------

From: Roland McGrath <roland@redhat.com>

commit 92dc07b1f988e8c237a38e23be660b9b8533e6fd upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/binfmt_elf.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)

--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1188,9 +1188,11 @@ static unsigned long vma_dump_size(struc
* 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.
*/
@@ -1203,7 +1205,15 @@ static unsigned long vma_dump_size(struc
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;
}