Address Sanitizer

Check for memory leaks, buffer overflows, etc

Note: Running a program using ASAN will consume more memory and run more slowly than normal.

The Address Sanitizer adds compile-time options that can detect:

  • Memory leaks
  • Buffer overflows (and underflows)
  • Out-of-bounds accesses to heap, stack and globals
  • Memory use after free
  • Double-free, invalid free


To build NeoMutt with the Address Sanitizer, you need to add a option to the compiler and linker. The simplest way is to:

./configure --asan [OPTIONS]

Alternatively, you can specify additional build flags:

export EXTRA_CFLAGS="-fsanitize=address"
export EXTRA_LDFLAGS="-fsanitize=address"
./configure [OPTIONS]

Address Sanitizer Options

The Address Sanitizer’s behaviour can be controlled by setting an environment variable. Multiple options should be separated with a colon :

Note: Some platforms will need to use this options to show memory leaks:

export ASAN_OPTIONS="detect_leaks=1"

This highly recommended option redirects the output to a file (ncurses can cause the output become garbled).

This will create a file called asan.PROCESS_ID

export ASAN_OPTIONS="log_path=asan"

This option reduces the clutter in the output:

export ASAN_OPTIONS="print_legend=0"

Here are multiple options together, separated by colon :

export ASAN_OPTIONS="print_legend=0:log_path=asan"

For a fuller list of options, see

Running NeoMutt

Now, run NeoMutt as normal.

If there are no memory problems, there will be no output from the Address Sanitizer.

Sample Output

Here’s some sample output from a couple of bugs:

Memory Leak

This shows a simple memory leak. It shows the callstack up to the point where the memory was allocated.

==61167==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 19 byte(s) in 1 object(s) allocated from:
    #0 0x7eff1fd87667 in __interceptor_malloc (/lib64/
    #1 0x741c95 in mutt_mem_malloc mutt/memory.c:95
    #2 0x48f089 in get_hostname /home/mutt/work/neo/init.c:343
    #3 0x49259e in mutt_init /home/mutt/work/neo/init.c:929
    #4 0x4a4caa in main /home/mutt/work/neo/main.c:665
    #5 0x7eff1ea1c041 in __libc_start_main ../csu/libc-start.c:308

SUMMARY: AddressSanitizer: 19 byte(s) leaked in 1 allocation(s).

Use After Free

This use-after-free example shows the callstack in three places:

  • Where the memory was just accessed
  • Where the memory was previously freed
  • Where the memory was originally allocated
==60945==ERROR: AddressSanitizer: heap-use-after-free on address 0x60300004e0d0 at pc 0x7fc99e346f85 bp 0x7ffe360a98f0 sp 0x7ffe360a9098
READ of size 2 at 0x60300004e0d0 thread T0
    #0 0x7fc99e346f84  (/lib64/
    #1 0x4a9b8e in main /home/mutt/work/neo/main.c:1277
    #2 0x7fc99d04b041 in __libc_start_main ../csu/libc-start.c:308
    #3 0x40d55d in _start (/home/mutt/work/neo/neomutt+0x40d55d)

0x60300004e0d0 is located 0 bytes inside of 25-byte region [0x60300004e0d0,0x60300004e0e9)
freed by thread T0 here:
    #0 0x7fc99e3b6307 in __interceptor_free (/lib64/
    #1 0x741c4f in mutt_mem_free mutt/memory.c:75
    #2 0x49151e in mutt_opts_free /home/mutt/work/neo/init.c:691
    #3 0x4a9b6b in main /home/mutt/work/neo/main.c:1273
    #4 0x7fc99d04b041 in __libc_start_main ../csu/libc-start.c:308

previously allocated by thread T0 here:
    #0 0x7fc99e3603a7 in strdup (/lib64/
    #1 0x74dae5 in mutt_str_dup mutt/string.c:375
    #2 0x74df41 in mutt_str_replace mutt/string.c:451
    #3 0x4a9091 in main /home/mutt/work/neo/main.c:1189
    #4 0x7fc99d04b041 in __libc_start_main ../csu/libc-start.c:308

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