[Crash-utility] [PATCH v2 3/3] Support core files with "unusual" layout
Mathias Krause
minipli at grsecurity.net
Sat Aug 8 15:17:38 UTC 2020
The netdump code not only gets used for netdump/diskdump files, but also
for kdump core files. These can also be generated with the 'vmss2core'
tool that'll produce a slightly different format that isn't as densely
packed as we expect it to be. In fact, the implicit assumption that the
ELF program headers directly follow the ELF header isn't always true for
these files, as they may contain the section headers in-between -- which
is totally conforming in regards to the ELF spec. This "padding" in
combination with the implicit assumption of densely packed headers make
us interpret the section headers as program headers which is obviously
wrong.
Support these kind of core files too by not blindly assuming the program
headers follow the ELF header directly but by looking at the program
header offset in the ELF header and use that instead. Add some guarding
sanity checks to decline operating on obviously malicious or broken core
files.
To not needlessly make things too complicated, allow a "padding space"
of up to 128 bytes only.
Signed-off-by: Mathias Krause <minipli at grsecurity.net>
---
netdump.c | 90 +++++++++++++++++++++++++++++++++++++------------------
netdump.h | 8 +++++
2 files changed, 69 insertions(+), 29 deletions(-)
diff --git a/netdump.c b/netdump.c
index 406416af36bf..7bbb914be01d 100644
--- a/netdump.c
+++ b/netdump.c
@@ -132,7 +132,7 @@ is_netdump(char *file, ulong source_query)
}
}
- size = MIN_NETDUMP_ELF_HEADER_SIZE;
+ size = SAFE_NETDUMP_ELF_HEADER_SIZE;
if ((eheader = (char *)malloc(size)) == NULL) {
fprintf(stderr, "cannot malloc minimum ELF header buffer\n");
clean_exit(1);
@@ -219,8 +219,22 @@ is_netdump(char *file, ulong source_query)
source_query))
goto bailout;
- load32 = (Elf32_Phdr *)
- &eheader[sizeof(Elf32_Ehdr)+sizeof(Elf32_Phdr)];
+ if (elf32->e_phoff != sizeof(Elf32_Ehdr)) {
+ if (CRASHDEBUG(1))
+ error(WARNING, "%s: first PHdr not following "
+ "EHdr (PHdr offset = %u)\n", file,
+ elf32->e_phoff);
+ /* it's okay as long as we've read enough data */
+ if (elf32->e_phoff > size - 2 * sizeof(Elf32_Phdr)) {
+ error(WARNING, "%s: PHdr to far into file!\n",
+ file);
+ goto bailout;
+ }
+ }
+
+ /* skip the NOTE program header */
+ load32 = (Elf32_Phdr *)
+ &eheader[elf32->e_phoff+sizeof(Elf32_Phdr)];
if ((load32->p_offset & (MIN_PAGE_SIZE-1)) ||
(load32->p_align == 0))
@@ -291,8 +305,22 @@ is_netdump(char *file, ulong source_query)
source_query))
goto bailout;
- load64 = (Elf64_Phdr *)
- &eheader[sizeof(Elf64_Ehdr)+sizeof(Elf64_Phdr)];
+ if (elf64->e_phoff != sizeof(Elf64_Ehdr)) {
+ if (CRASHDEBUG(1))
+ error(WARNING, "%s: first PHdr not following "
+ "EHdr (PHdr offset = %u)\n", file,
+ elf64->e_phoff);
+ /* it's okay as long as we've read enough data */
+ if (elf64->e_phoff > size - 2 * sizeof(Elf64_Phdr)) {
+ error(WARNING, "%s: PHdr to far into file!\n",
+ file);
+ goto bailout;
+ }
+ }
+
+ /* skip the NOTE program header */
+ load64 = (Elf64_Phdr *)
+ &eheader[elf64->e_phoff+sizeof(Elf64_Phdr)];
if ((load64->p_offset & (MIN_PAGE_SIZE-1)) ||
(load64->p_align == 0))
@@ -352,10 +380,9 @@ is_netdump(char *file, ulong source_query)
fprintf(stderr, "cannot malloc PT_LOAD segment buffers\n");
clean_exit(1);
}
- nd->notes32 = (Elf32_Phdr *)
- &nd->elf_header[sizeof(Elf32_Ehdr)];
- nd->load32 = (Elf32_Phdr *)
- &nd->elf_header[sizeof(Elf32_Ehdr)+sizeof(Elf32_Phdr)];
+ nd->notes32 = (Elf32_Phdr *)
+ &nd->elf_header[nd->elf32->e_phoff];
+ nd->load32 = nd->notes32 + 1;
if (format == NETDUMP_ELF32)
nd->page_size = (uint)nd->load32->p_align;
dump_Elf32_Ehdr(nd->elf32);
@@ -391,10 +418,9 @@ is_netdump(char *file, ulong source_query)
fprintf(stderr, "cannot malloc PT_LOAD segment buffers\n");
clean_exit(1);
}
- nd->notes64 = (Elf64_Phdr *)
- &nd->elf_header[sizeof(Elf64_Ehdr)];
- nd->load64 = (Elf64_Phdr *)
- &nd->elf_header[sizeof(Elf64_Ehdr)+sizeof(Elf64_Phdr)];
+ nd->notes64 = (Elf64_Phdr *)
+ &nd->elf_header[nd->elf64->e_phoff];
+ nd->load64 = nd->notes64 + 1;
if (format == NETDUMP_ELF64)
nd->page_size = (uint)nd->load64->p_align;
dump_Elf64_Ehdr(nd->elf64);
@@ -469,8 +495,8 @@ resize_elf_header(int fd, char *file, char **eheader_ptr, char **sect0_ptr,
case NETDUMP_ELF32:
case KDUMP_ELF32:
num_pt_load_segments = elf32->e_phnum - 1;
- header_size = sizeof(Elf32_Ehdr) + sizeof(Elf32_Phdr) +
- (sizeof(Elf32_Phdr) * num_pt_load_segments);
+ header_size = MAX(sizeof(Elf32_Ehdr), elf32->e_phoff) +
+ (sizeof(Elf32_Phdr) * (num_pt_load_segments + 1));
break;
case NETDUMP_ELF64:
@@ -513,8 +539,8 @@ resize_elf_header(int fd, char *file, char **eheader_ptr, char **sect0_ptr,
} else
num_pt_load_segments = elf64->e_phnum - 1;
- header_size = sizeof(Elf64_Ehdr) + sizeof(Elf64_Phdr) +
- (sizeof(Elf64_Phdr) * num_pt_load_segments);
+ header_size = MAX(sizeof(Elf64_Ehdr), elf64->e_phoff) +
+ (sizeof(Elf64_Phdr) * (num_pt_load_segments + 1));
break;
}
@@ -544,7 +570,7 @@ resize_elf_header(int fd, char *file, char **eheader_ptr, char **sect0_ptr,
{
case NETDUMP_ELF32:
case KDUMP_ELF32:
- load32 = (Elf32_Phdr *)&eheader[sizeof(Elf32_Ehdr)+sizeof(Elf32_Phdr)];
+ load32 = (Elf32_Phdr *)&eheader[elf32->e_phoff+sizeof(Elf32_Phdr)];
p_offset32 = load32->p_offset;
for (i = 0; i < num_pt_load_segments; i++, load32 += 1) {
if (load32->p_offset &&
@@ -556,7 +582,7 @@ resize_elf_header(int fd, char *file, char **eheader_ptr, char **sect0_ptr,
case NETDUMP_ELF64:
case KDUMP_ELF64:
- load64 = (Elf64_Phdr *)&eheader[sizeof(Elf64_Ehdr)+sizeof(Elf64_Phdr)];
+ load64 = (Elf64_Phdr *)&eheader[elf64->e_phoff+sizeof(Elf64_Phdr)];
p_offset64 = load64->p_offset;
for (i = 0; i < num_pt_load_segments; i++, load64 += 1) {
if (load64->p_offset &&
@@ -4459,8 +4485,12 @@ proc_kcore_init_32(FILE *fp, int kcore_fd)
close(fd);
elf32 = (Elf32_Ehdr *)&eheader[0];
- notes32 = (Elf32_Phdr *)&eheader[sizeof(Elf32_Ehdr)];
- load32 = (Elf32_Phdr *)&eheader[sizeof(Elf32_Ehdr)+sizeof(Elf32_Phdr)];
+ if (elf32->e_phoff > sizeof(eheader) - 2 * sizeof(Elf32_Phdr)) {
+ error(INFO, "/proc/kcore: ELF program header offset too big!\n");
+ return FALSE;
+ }
+ notes32 = (Elf32_Phdr *)&eheader[elf32->e_phoff];
+ load32 = notes32 + 1;
pkd->segments = elf32->e_phnum - 1;
@@ -4479,9 +4509,8 @@ proc_kcore_init_32(FILE *fp, int kcore_fd)
}
BCOPY(&eheader[0], &pkd->elf_header[0], pkd->header_size);
- pkd->notes32 = (Elf32_Phdr *)&pkd->elf_header[sizeof(Elf32_Ehdr)];
- pkd->load32 = (Elf32_Phdr *)
- &pkd->elf_header[sizeof(Elf32_Ehdr)+sizeof(Elf32_Phdr)];
+ pkd->notes32 = (Elf32_Phdr *)&pkd->elf_header[elf32->e_phoff];
+ pkd->load32 = pkd->notes32 + 1;
pkd->flags |= KCORE_ELF32;
kcore_memory_dump(CRASHDEBUG(1) ? fp : pc->nullfp);
@@ -4529,8 +4558,12 @@ proc_kcore_init_64(FILE *fp, int kcore_fd)
close(fd);
elf64 = (Elf64_Ehdr *)&eheader[0];
- notes64 = (Elf64_Phdr *)&eheader[sizeof(Elf64_Ehdr)];
- load64 = (Elf64_Phdr *)&eheader[sizeof(Elf64_Ehdr)+sizeof(Elf64_Phdr)];
+ if (elf64->e_phoff > sizeof(eheader) - 2 * sizeof(Elf64_Phdr)) {
+ error(INFO, "/proc/kcore: ELF program header offset too big!\n");
+ return FALSE;
+ }
+ notes64 = (Elf64_Phdr *)&eheader[elf64->e_phoff];
+ load64 = notes64 + 1;
pkd->segments = elf64->e_phnum - 1;
@@ -4550,9 +4583,8 @@ proc_kcore_init_64(FILE *fp, int kcore_fd)
}
BCOPY(&eheader[0], &pkd->elf_header[0], pkd->header_size);
- pkd->notes64 = (Elf64_Phdr *)&pkd->elf_header[sizeof(Elf64_Ehdr)];
- pkd->load64 = (Elf64_Phdr *)
- &pkd->elf_header[sizeof(Elf64_Ehdr)+sizeof(Elf64_Phdr)];
+ pkd->notes64 = (Elf64_Phdr *)&pkd->elf_header[elf64->e_phoff];
+ pkd->load64 = pkd->notes64 + 1;
pkd->flags |= KCORE_ELF64;
kcore_memory_dump(CRASHDEBUG(1) ? fp : pc->nullfp);
diff --git a/netdump.h b/netdump.h
index 7fa04f7c3a0f..ffd60b8d5021 100644
--- a/netdump.h
+++ b/netdump.h
@@ -26,6 +26,14 @@
#define MIN_NETDUMP_ELF_HEADER_SIZE \
MAX(MIN_NETDUMP_ELF32_HEADER_SIZE, MIN_NETDUMP_ELF64_HEADER_SIZE)
+#define NETDUMP_ELF_HEADER_SPARE_SIZE 128
+/*
+ * "Safe" size, as in covering the ELF header and the first two program headers
+ * plus any "padding" in-between, like section headers.
+ */
+#define SAFE_NETDUMP_ELF_HEADER_SIZE \
+ (MIN_NETDUMP_ELF_HEADER_SIZE+NETDUMP_ELF_HEADER_SPARE_SIZE)
+
#define NT_TASKSTRUCT 4
#define NT_DISKDUMP 0x70000001
--
2.20.1
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