From e11815bb7f0656f39e122073e0e3284ec7f5d021 Mon Sep 17 00:00:00 2001
From: Mike Frysinger <vapier@gentoo.org>
Date: Tue, 29 Mar 2016 23:35:44 -0400
Subject: [PATCH] libsandbox: fix symtab walking with some ELFs
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The strtab assumption works if there is no SysV hash table.
Add logic to handle that scenario.

URL: https://bugs.gentoo.org/578524
Reported-by: Toralf Förster <toralf.foerster@gmx.de>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
---
 libsandbox/wrapper-funcs/__wrapper_exec.c | 30 +++++++++++++++++-------------
 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/libsandbox/wrapper-funcs/__wrapper_exec.c b/libsandbox/wrapper-funcs/__wrapper_exec.c
index f7f51ab..d372366 100644
--- a/libsandbox/wrapper-funcs/__wrapper_exec.c
+++ b/libsandbox/wrapper-funcs/__wrapper_exec.c
@@ -83,10 +83,10 @@ static bool sb_check_exec(const char *filename, char *const argv[])
 ({ \
 	Elf##n##_Ehdr *ehdr = (void *)elf; \
 	Elf##n##_Phdr *phdr = (void *)(elf + ehdr->e_phoff); \
-	Elf##n##_Addr vaddr, filesz, vsym = 0, vstr = 0; \
-	Elf##n##_Off offset, symoff = 0, stroff = 0; \
+	Elf##n##_Addr vaddr, filesz, vsym = 0, vstr = 0, vhash = 0; \
+	Elf##n##_Off offset, symoff = 0, stroff = 0, hashoff = 0; \
 	Elf##n##_Dyn *dyn; \
-	Elf##n##_Sym *sym; \
+	Elf##n##_Sym *sym, *symend; \
 	uint##n##_t ent_size = 0, str_size = 0; \
 	bool dynamic = false; \
 	size_t i; \
@@ -106,6 +106,7 @@ static bool sb_check_exec(const char *filename, char *const argv[])
 				case DT_SYMENT: ent_size = dyn->d_un.d_val; break; \
 				case DT_STRTAB: vstr = dyn->d_un.d_val; break; \
 				case DT_STRSZ:  str_size = dyn->d_un.d_val; break; \
+				case DT_HASH:   vhash = dyn->d_un.d_val; break; \
 				} \
 				++dyn; \
 			} \
@@ -123,6 +124,8 @@ static bool sb_check_exec(const char *filename, char *const argv[])
 				symoff = offset + (vsym - vaddr); \
 			if (vstr >= vaddr && vstr < vaddr + filesz) \
 				stroff = offset + (vstr - vaddr); \
+			if (vhash >= vaddr && vhash < vaddr + filesz) \
+				hashoff = offset + (vhash - vaddr); \
 		} \
 		\
 		/* Finally walk the symbol table.  This should generally be fast as \
@@ -130,18 +133,20 @@ static bool sb_check_exec(const char *filename, char *const argv[])
 		 * out there do not export any symbols at all. \
 		 */ \
 		if (symoff && stroff) { \
-			sym = (void *)(elf + symoff); \
+			/* Hash entries are always 32-bits. */ \
+			uint32_t *hashes = (void *)(elf + hashoff); \
 			/* Nowhere is the # of symbols recorded, or the size of the symbol \
-			 * table.  Instead, we do what glibc does: assume that the string \
-			 * table always follows the symbol table.  This seems like a poor \
-			 * assumption to make, but glibc has gotten by this long.  We could \
-			 * rely on DT_HASH and walking all the buckets to find the largest \
-			 * symbol index, but that's also a bit hacky. \
+			 * table.  Instead, we do what glibc does: use the sysv hash table \
+			 * if it exists, else assume that the string table always directly \
+			 * follows the symbol table.  This seems like a poor assumption to \
+			 * make, but glibc has gotten by this long. \
 			 * \
 			 * We don't sanity check the ranges here as you aren't executing \
 			 * corrupt programs in the sandbox. \
 			 */ \
-			for (i = 0; i < (vstr - vsym) / ent_size; ++i) { \
+			sym = (void *)(elf + symoff); \
+			symend = vhash ? (sym + hashes[1]) : (void *)(elf + stroff); \
+			while (sym < symend) { \
 				char *symname = (void *)(elf + stroff + sym->st_name); \
 				if (ELF##n##_ST_VISIBILITY(sym->st_other) == STV_DEFAULT && \
 				    sym->st_shndx != SHN_UNDEF && sym->st_shndx < SHN_LORESERVE && \
@@ -149,9 +154,8 @@ static bool sb_check_exec(const char *filename, char *const argv[])
 				    /* Minor optimization to avoid strcmp. */ \
 				    symname[0] == '_' && symname[1] == '_') { \
 					/* Blacklist internal C library symbols. */ \
-					size_t j; \
-					for (j = 0; j < ARRAY_SIZE(libc_alloc_syms); ++j) \
-						if (!strcmp(symname, libc_alloc_syms[j])) { \
+					for (i = 0; i < ARRAY_SIZE(libc_alloc_syms); ++i) \
+						if (!strcmp(symname, libc_alloc_syms[i])) { \
 							run_in_process = false; \
 							goto use_trace; \
 						} \
-- 
2.7.4