[PATCH RFT] objtool: Validate find symtab in elf_create_rela_section()

[Robertus Diawan Chris <robertusdchris@gmail.com>]

find_section_by_name() will return NULL if the section is not found. If
the symtab section is not found, using the return value of
find_section_by_name() directly will cause null pointer dereference. So
check the return value from find_section_by_name() when finding symtab
section before using the information.

This is reported by Coverity Scan with CID 1445573 as NULL_RETURNS.

Fixes: 627fce14809b ("objtool: Add ORC unwind table generation")
Signed-off-by: Robertus Diawan Chris <robertusdchris@gmail.com>
---
Currently still not sure _when_ symtab section is not found. This is
reported by static analysis tool, which can be wrong. I apologize if
this turns out to be false positive.

 tools/objtool/elf.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index f3df2bde119f..ce7246d3b302 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -1625,7 +1625,7 @@ static int elf_alloc_reloc(struct elf *elf, struct section *rsec)
 struct section *elf_create_rela_section(struct elf *elf, struct section *sec,
 					unsigned int nr_relocs)
 {
-	struct section *rsec;
+	struct section *rsec, *symtab;
 	char *rsec_name;
 
 	rsec_name = malloc(strlen(sec->name) + strlen(".rela") + 1);
@@ -1654,7 +1654,13 @@ struct section *elf_create_rela_section(struct elf *elf, struct section *sec,
 		}
 	}
 
-	rsec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
+	symtab = find_section_by_name(elf, ".symtab");
+	if (!symtab) {
+		ERROR("can't find .symtab");
+		return NULL;
+	}
+
+	rsec->sh.sh_link = symtab->idx;
 	rsec->sh.sh_info = sec->idx;
 
 	sec->rsec = rsec;

base-commit: 254f49634ee16a731174d2ae34bc50bd5f45e731
-- 
2.54.0