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authorAkira Kawata <akirakawata1@gmail.com>2022-01-27 13:40:16 +0100
committerKees Cook <keescook@chromium.org>2022-03-02 01:16:27 +0100
commit0da1d5002745cdc721bc018b582a8a9704d56c42 (patch)
tree7b0584635f927251d3306f8092548eb4b7e30bf2 /fs/binfmt_elf.c
parentbinfmt: move more stuff undef CONFIG_COREDUMP (diff)
downloadlinux-0da1d5002745cdc721bc018b582a8a9704d56c42.tar.xz
linux-0da1d5002745cdc721bc018b582a8a9704d56c42.zip
fs/binfmt_elf: Fix AT_PHDR for unusual ELF files
BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=197921 As pointed out in the discussion of buglink, we cannot calculate AT_PHDR as the sum of load_addr and exec->e_phoff. : The AT_PHDR of ELF auxiliary vectors should point to the memory address : of program header. But binfmt_elf.c calculates this address as follows: : : NEW_AUX_ENT(AT_PHDR, load_addr + exec->e_phoff); : : which is wrong since e_phoff is the file offset of program header and : load_addr is the memory base address from PT_LOAD entry. : : The ld.so uses AT_PHDR as the memory address of program header. In normal : case, since the e_phoff is usually 64 and in the first PT_LOAD region, it : is the correct program header address. : : But if the address of program header isn't equal to the first PT_LOAD : address + e_phoff (e.g. Put the program header in other non-consecutive : PT_LOAD region), ld.so will try to read program header from wrong address : then crash or use incorrect program header. This is because exec->e_phoff is the offset of PHDRs in the file and the address of PHDRs in the memory may differ from it. This patch fixes the bug by calculating the address of program headers from PT_LOADs directly. Signed-off-by: Akira Kawata <akirakawata1@gmail.com> Reported-by: kernel test robot <lkp@intel.com> Acked-by: Kees Cook <keescook@chromium.org> Signed-off-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20220127124014.338760-2-akirakawata1@gmail.com
Diffstat (limited to 'fs/binfmt_elf.c')
-rw-r--r--fs/binfmt_elf.c24
1 files changed, 18 insertions, 6 deletions
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index d0c1703b9576..600cec2173c8 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -172,8 +172,8 @@ static int padzero(unsigned long elf_bss)
static int
create_elf_tables(struct linux_binprm *bprm, const struct elfhdr *exec,
- unsigned long load_addr, unsigned long interp_load_addr,
- unsigned long e_entry)
+ unsigned long interp_load_addr,
+ unsigned long e_entry, unsigned long phdr_addr)
{
struct mm_struct *mm = current->mm;
unsigned long p = bprm->p;
@@ -259,7 +259,7 @@ create_elf_tables(struct linux_binprm *bprm, const struct elfhdr *exec,
NEW_AUX_ENT(AT_HWCAP, ELF_HWCAP);
NEW_AUX_ENT(AT_PAGESZ, ELF_EXEC_PAGESIZE);
NEW_AUX_ENT(AT_CLKTCK, CLOCKS_PER_SEC);
- NEW_AUX_ENT(AT_PHDR, load_addr + exec->e_phoff);
+ NEW_AUX_ENT(AT_PHDR, phdr_addr);
NEW_AUX_ENT(AT_PHENT, sizeof(struct elf_phdr));
NEW_AUX_ENT(AT_PHNUM, exec->e_phnum);
NEW_AUX_ENT(AT_BASE, interp_load_addr);
@@ -824,7 +824,7 @@ static int parse_elf_properties(struct file *f, const struct elf_phdr *phdr,
static int load_elf_binary(struct linux_binprm *bprm)
{
struct file *interpreter = NULL; /* to shut gcc up */
- unsigned long load_addr = 0, load_bias = 0;
+ unsigned long load_addr, load_bias = 0, phdr_addr = 0;
int load_addr_set = 0;
unsigned long error;
struct elf_phdr *elf_ppnt, *elf_phdata, *interp_elf_phdata = NULL;
@@ -1181,6 +1181,17 @@ out_free_interp:
reloc_func_desc = load_bias;
}
}
+
+ /*
+ * Figure out which segment in the file contains the Program
+ * Header table, and map to the associated memory address.
+ */
+ if (elf_ppnt->p_offset <= elf_ex->e_phoff &&
+ elf_ex->e_phoff < elf_ppnt->p_offset + elf_ppnt->p_filesz) {
+ phdr_addr = elf_ex->e_phoff - elf_ppnt->p_offset +
+ elf_ppnt->p_vaddr;
+ }
+
k = elf_ppnt->p_vaddr;
if ((elf_ppnt->p_flags & PF_X) && k < start_code)
start_code = k;
@@ -1216,6 +1227,7 @@ out_free_interp:
}
e_entry = elf_ex->e_entry + load_bias;
+ phdr_addr += load_bias;
elf_bss += load_bias;
elf_brk += load_bias;
start_code += load_bias;
@@ -1279,8 +1291,8 @@ out_free_interp:
goto out;
#endif /* ARCH_HAS_SETUP_ADDITIONAL_PAGES */
- retval = create_elf_tables(bprm, elf_ex,
- load_addr, interp_load_addr, e_entry);
+ retval = create_elf_tables(bprm, elf_ex, interp_load_addr,
+ e_entry, phdr_addr);
if (retval < 0)
goto out;