Commit 2217b982 authored by Max Filippov's avatar Max Filippov Committed by Greg Ungerer
Browse files

binfmt_flat: revert "binfmt_flat: don't offset the data start" 



binfmt_flat loader uses the gap between text and data to store data
segment pointers for the libraries. Even in the absence of shared
libraries it stores at least one pointer to the executable's own data
segment. Text and data can go back to back in the flat binary image and
without offsetting data segment last few instructions in the text
segment may get corrupted by the data segment pointer.

Fix it by reverting commit a2357223 ("binfmt_flat: don't offset the
data start").

Cc: stable@vger.kernel.org
Fixes: a2357223 ("binfmt_flat: don't offset the data start")
Signed-off-by: default avatarMax Filippov <jcmvbkbc@gmail.com>
Signed-off-by: default avatarGreg Ungerer <gerg@linux-m68k.org>
parent d012a719

fs/binfmt_flat.c

+12 −8
Original line number Diff line number Diff line
@@ -576,7 +576,7 @@ static int load_flat_file(struct linux_binprm *bprm, 
			goto err;

		}



		len = data_len + extra;

		len = data_len + extra + MAX_SHARED_LIBS * sizeof(unsigned long);

		len = PAGE_ALIGN(len);

		realdatastart = vm_mmap(NULL, 0, len,

			PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE, 0);
@@ -590,7 +590,9 @@ static int load_flat_file(struct linux_binprm *bprm, 
			vm_munmap(textpos, text_len);

			goto err;

		}

		datapos = ALIGN(realdatastart, FLAT_DATA_ALIGN);

		datapos = ALIGN(realdatastart +

				MAX_SHARED_LIBS * sizeof(unsigned long),

				FLAT_DATA_ALIGN);



		pr_debug("Allocated data+bss+stack (%u bytes): %lx\n",

			 data_len + bss_len + stack_len, datapos);
@@ -620,7 +622,7 @@ static int load_flat_file(struct linux_binprm *bprm, 
		memp_size = len;

	} else {



		len = text_len + data_len + extra;

		len = text_len + data_len + extra + MAX_SHARED_LIBS * sizeof(u32);

		len = PAGE_ALIGN(len);

		textpos = vm_mmap(NULL, 0, len,

			PROT_READ | PROT_EXEC | PROT_WRITE, MAP_PRIVATE, 0);
@@ -635,7 +637,9 @@ static int load_flat_file(struct linux_binprm *bprm, 
		}



		realdatastart = textpos + ntohl(hdr->data_start);

		datapos = ALIGN(realdatastart, FLAT_DATA_ALIGN);

		datapos = ALIGN(realdatastart +

				MAX_SHARED_LIBS * sizeof(u32),

				FLAT_DATA_ALIGN);



		reloc = (__be32 __user *)

			(datapos + (ntohl(hdr->reloc_start) - text_len));
@@ -652,7 +656,6 @@ static int load_flat_file(struct linux_binprm *bprm, 
					 (text_len + full_data

						  - sizeof(struct flat_hdr)),

					 0);

			if (datapos != realdatastart)

			memmove((void *) datapos, (void *) realdatastart,

					full_data);

#else
@@ -710,7 +713,8 @@ static int load_flat_file(struct linux_binprm *bprm, 
		if (IS_ERR_VALUE(result)) {

			ret = result;

			pr_err("Unable to read code+data+bss, errno %d\n", ret);

			vm_munmap(textpos, text_len + data_len + extra);

			vm_munmap(textpos, text_len + data_len + extra +

				MAX_SHARED_LIBS * sizeof(u32));

			goto err;

		}

	}

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