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Commit 92dc07b1 authored by Roland McGrath's avatar Roland McGrath
Browse files

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: default avatarGerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: default avatarRoland McGrath <roland@redhat.com>
parent 6cec5083

fs/binfmt_elf.c

+12 −2
Original line number Diff line number Diff line
@@ -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;

	}