elf: enforce MAP_FIXED on overlaying elf segments

Anshuman has reported that with "fs, elf: drop MAP_FIXED usage from
elf_map" applied, some ELF binaries in his environment fail to start
with

 [   23.423642] 9148 (sed): Uhuuh, elf segment at 0000000010030000 requested but the memory is mapped already
 [   23.423706] requested [10030000, 10040000] mapped [10030000, 10040000] 100073 anon

The reason is that the above binary has overlapping elf segments:

  LOAD           0x0000000000000000 0x0000000010000000 0x0000000010000000
                 0x0000000000013a8c 0x0000000000013a8c  R E    10000
  LOAD           0x000000000001fd40 0x000000001002fd40 0x000000001002fd40
                 0x00000000000002c0 0x00000000000005e8  RW     10000
  LOAD           0x0000000000020328 0x0000000010030328 0x0000000010030328
                 0x0000000000000384 0x00000000000094a0  RW     10000

That binary has two RW LOAD segments, the first crosses a page border
into the second

  0x1002fd40 (LOAD2-vaddr) + 0x5e8 (LOAD2-memlen) == 0x10030328 (LOAD3-vaddr)

Handle this situation by enforcing MAP_FIXED when we establish a
temporary brk VMA to handle overlapping segments.  All other mappings
will still use MAP_FIXED_NOREPLACE.

Link: http://lkml.kernel.org/r/20180213100440.GM3443@dhcp22.suse.cz
Signed-off-by: Michal Hocko <mhocko@suse.com>
Reported-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Reviewed-by: Khalid Aziz <khalid.aziz@oracle.com>
Cc: Andrei Vagin <avagin@openvz.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Kees Cook <keescook@chromium.org>
Cc: Abdul Haleem <abdhalee@linux.vnet.ibm.com>
Cc: Joel Stanley <joel@jms.id.au>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Mark Brown <broonie@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 3 deletions

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 46f0438088d3..41e04183e4ce 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -895,7 +895,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
            the correct location in memory. */
         for(i = 0, elf_ppnt = elf_phdata;
             i < loc->elf_ex.e_phnum; i++, elf_ppnt++) {
-                int elf_prot = 0, elf_flags;
+                int elf_prot = 0, elf_flags, elf_fixed = MAP_FIXED_NOREPLACE;
                 unsigned long k, vaddr;
                 unsigned long total_size = 0;
 
@@ -927,6 +927,13 @@ static int load_elf_binary(struct linux_binprm *bprm)
                                          */
                                 }
                         }
+
+                        /*
+                         * Some binaries have overlapping elf segments and then
+                         * we have to forcefully map over an existing mapping
+                         * e.g. over this newly established brk mapping.
+                         */
+                        elf_fixed = MAP_FIXED;
                 }
 
                 if (elf_ppnt->p_flags & PF_R)
@@ -944,7 +951,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
                  * the ET_DYN load_addr calculations, proceed normally.
                  */
                 if (loc->elf_ex.e_type == ET_EXEC || load_addr_set) {
-                        elf_flags |= MAP_FIXED_NOREPLACE;
+                        elf_flags |= elf_fixed;
                 } else if (loc->elf_ex.e_type == ET_DYN) {
                         /*
                          * This logic is run once for the first LOAD Program
@@ -980,7 +987,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
                                 load_bias = ELF_ET_DYN_BASE;
                                 if (current->flags & PF_RANDOMIZE)
                                         load_bias += arch_mmap_rnd();
-                                elf_flags |= MAP_FIXED_NOREPLACE;
+                                elf_flags |= elf_fixed;
                         } else
                                 load_bias = 0;