[PATCH 4/7] binfmt_elf: remove the set_fs(KERNEL_DS) in elf_core_dump

Christoph Hellwig
2020-04-21T15:42:59Z

There is no logic in elf_core_dump itself, or in the various arch helpers
called from it which use uaccess routines on kernel pointers except for
the file writes thate are nicely encapsulated by using __kernel_write in
dump_emit.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
fs/binfmt_elf.c | 40 +++++++++++++---------------------------
1 file changed, 13 insertions(+), 27 deletions(-)

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index a1f57e20c3cf..b29b84595b09 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1355,7 +1355,6 @@ static unsigned long vma_dump_size(struct vm_area_struct *vma,
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.
*/
@@ -1368,14 +1367,8 @@ 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;
- /*
- * 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;
}
@@ -2183,7 +2176,6 @@ static void fill_extnum_info(struct elfhdr *elf, struct elf_shdr *shdr4extnum,
static int elf_core_dump(struct coredump_params *cprm)
{
int has_dumped = 0;
- mm_segment_t fs;
int segs, i;
size_t vma_data_size = 0;
struct vm_area_struct *vma, *gate_vma;
@@ -2236,9 +2228,6 @@ static int elf_core_dump(struct coredump_params *cprm)

has_dumped = 1;

- fs = get_fs();
- set_fs(KERNEL_DS);
-
offset += sizeof(elf); /* Elf header */
offset += segs * sizeof(struct elf_phdr); /* Program headers */

@@ -2250,7 +2239,7 @@ static int elf_core_dump(struct coredump_params *cprm)

phdr4note = kmalloc(sizeof(*phdr4note), GFP_KERNEL);
if (!phdr4note)
- goto end_coredump;
+ goto cleanup;

fill_elf_note_phdr(phdr4note, sz, offset);
offset += sz;
@@ -2265,7 +2254,7 @@ static int elf_core_dump(struct coredump_params *cprm)
vma_filesz = kvmalloc(array_size(sizeof(*vma_filesz), (segs - 1)),
GFP_KERNEL);
if (!vma_filesz)
- goto end_coredump;
+ goto cleanup;

for (i = 0, vma = first_vma(current, gate_vma); vma != NULL;
vma = next_vma(vma, gate_vma)) {
@@ -2283,17 +2272,17 @@ static int elf_core_dump(struct coredump_params *cprm)
if (e_phnum == PN_XNUM) {
shdr4extnum = kmalloc(sizeof(*shdr4extnum), GFP_KERNEL);
if (!shdr4extnum)
- goto end_coredump;
+ goto cleanup;
fill_extnum_info(&elf, shdr4extnum, e_shoff, segs);
}

offset = dataoff;

if (!dump_emit(cprm, &elf, sizeof(elf)))
- goto end_coredump;
+ goto cleanup;

if (!dump_emit(cprm, phdr4note, sizeof(*phdr4note)))
- goto end_coredump;
+ goto cleanup;

/* Write program headers for segments dump */
for (i = 0, vma = first_vma(current, gate_vma); vma != NULL;
@@ -2315,22 +2304,22 @@ static int elf_core_dump(struct coredump_params *cprm)
phdr.p_align = ELF_EXEC_PAGESIZE;

if (!dump_emit(cprm, &phdr, sizeof(phdr)))
- goto end_coredump;
+ goto cleanup;
}

if (!elf_core_write_extra_phdrs(cprm, offset))
- goto end_coredump;
+ goto cleanup;

/* write out the notes section */
if (!write_note_info(&info, cprm))
- goto end_coredump;
+ goto cleanup;

if (elf_coredump_extra_notes_write(cprm))
- goto end_coredump;
+ goto cleanup;

/* Align to page */
if (!dump_skip(cprm, dataoff - cprm->pos))
- goto end_coredump;
+ goto cleanup;

for (i = 0, vma = first_vma(current, gate_vma); vma != NULL;
vma = next_vma(vma, gate_vma)) {
@@ -2352,22 +2341,19 @@ static int elf_core_dump(struct coredump_params *cprm)
} else
stop = !dump_skip(cprm, PAGE_SIZE);
if (stop)
- goto end_coredump;
+ goto cleanup;
}
}
dump_truncate(cprm);

if (!elf_core_write_extra_data(cprm))
- goto end_coredump;
+ goto cleanup;

if (e_phnum == PN_XNUM) {
if (!dump_emit(cprm, shdr4extnum, sizeof(*shdr4extnum)))
- goto end_coredump;
+ goto cleanup;
}

-end_coredump:
- set_fs(fs);
-
cleanup:
free_note_info(&info);
kfree(shdr4extnum);
--
2.26.1