Fix computations with (potentially) NULL pointer

When map_address is NULL, computing map_address+offset is technically
undefined behavior, and triggers Clang/LLVM warning when using
-fsanitize=pointer-overflow.

Fix this by using uintptr_t to perform computations.

Signed-off-by: Shahriar "Nafi" Rouf <nafi@google.com>
Signed-off-by: Paul Pluzhnikov <ppluzhnikov@google.com>

diff --git a/libelf/elf_begin.c b/libelf/elf_begin.c
index fe8c640a8107d941deed62ec9cee8fcf012e585c..9f8196b6dc0167698450e36715cec78461fba3fa 100644 (file)
--- a/libelf/elf_begin.c
+++ b/libelf/elf_begin.c
@@ -341,15 +341,15 @@ file_read_elf (int fildes, void *map_address, unsigned char *e_ident,
     {
       /* This pointer might not be directly usable if the alignment is
         not sufficient for the architecture.  */
-      Elf32_Ehdr *ehdr = (Elf32_Ehdr *) ((char *) map_address + offset);
+      uintptr_t ehdr = (uintptr_t) map_address + offset;
 
       /* This is a 32-bit binary.  */
       if (map_address != NULL && e_ident[EI_DATA] == MY_ELFDATA
          && (ALLOW_UNALIGNED
-             || (((uintptr_t) ehdr) & (__alignof__ (Elf32_Ehdr) - 1)) == 0))
+             || (ehdr & (__alignof__ (Elf32_Ehdr) - 1)) == 0))
        {
          /* We can use the mmapped memory.  */
-         elf->state.elf32.ehdr = ehdr;
+         elf->state.elf32.ehdr = (Elf32_Ehdr *) ehdr;
        }
       else
        {
@@ -382,8 +382,7 @@ file_read_elf (int fildes, void *map_address, unsigned char *e_ident,
       if (map_address != NULL && e_ident[EI_DATA] == MY_ELFDATA
          && cmd != ELF_C_READ_MMAP /* We need a copy to be able to write.  */
          && (ALLOW_UNALIGNED
-             || ((((uintptr_t) ehdr + e_shoff)
-                  & (__alignof__ (Elf32_Shdr) - 1)) == 0)))
+             || (((ehdr + e_shoff) & (__alignof__ (Elf32_Shdr) - 1)) == 0)))
        {
          if (unlikely (scncnt > 0 && e_shoff >= maxsize)
              || unlikely (maxsize - e_shoff
@@ -396,8 +395,7 @@ file_read_elf (int fildes, void *map_address, unsigned char *e_ident,
            }
 
          if (scncnt > 0)
-           elf->state.elf32.shdr
-             = (Elf32_Shdr *) ((char *) ehdr + e_shoff);
+           elf->state.elf32.shdr = (Elf32_Shdr *) (ehdr + e_shoff);
 
          for (size_t cnt = 0; cnt < scncnt; ++cnt)
            {
@@ -445,15 +443,15 @@ file_read_elf (int fildes, void *map_address, unsigned char *e_ident,
     {
       /* This pointer might not be directly usable if the alignment is
         not sufficient for the architecture.  */
-      Elf64_Ehdr *ehdr = (Elf64_Ehdr *) ((char *) map_address + offset);
+      uintptr_t ehdr = (uintptr_t) map_address + offset;
 
       /* This is a 64-bit binary.  */
       if (map_address != NULL && e_ident[EI_DATA] == MY_ELFDATA
          && (ALLOW_UNALIGNED
-             || (((uintptr_t) ehdr) & (__alignof__ (Elf64_Ehdr) - 1)) == 0))
+             || (ehdr & (__alignof__ (Elf64_Ehdr) - 1)) == 0))
        {
          /* We can use the mmapped memory.  */
-         elf->state.elf64.ehdr = ehdr;
+         elf->state.elf64.ehdr = (Elf64_Ehdr *) ehdr;
        }
       else
        {
@@ -486,8 +484,7 @@ file_read_elf (int fildes, void *map_address, unsigned char *e_ident,
       if (map_address != NULL && e_ident[EI_DATA] == MY_ELFDATA
          && cmd != ELF_C_READ_MMAP /* We need a copy to be able to write.  */
          && (ALLOW_UNALIGNED
-             || ((((uintptr_t) ehdr + e_shoff)
-                  & (__alignof__ (Elf64_Shdr) - 1)) == 0)))
+             || (((ehdr + e_shoff) & (__alignof__ (Elf64_Shdr) - 1)) == 0)))
        {
          if (unlikely (scncnt > 0 && e_shoff >= maxsize)
              || unlikely (maxsize - e_shoff
@@ -495,8 +492,7 @@ file_read_elf (int fildes, void *map_address, unsigned char *e_ident,
            goto free_and_out;
 
          if (scncnt > 0)
-           elf->state.elf64.shdr
-             = (Elf64_Shdr *) ((char *) ehdr + e_shoff);
+           elf->state.elf64.shdr = (Elf64_Shdr *) (ehdr + e_shoff);
 
          for (size_t cnt = 0; cnt < scncnt; ++cnt)
            {